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Am I understanding this correctly?

Someone did a plant survey in Angola in order to determine the ratios of bioavailable strontium isotopes in the region, and that data is to be used in comparison to the ratios of strontium isotopes found in "human enamel" (teeth? bones?) in the skeletons of slaves? And this data can suggest to researchers the origins of individual slaves, and at a larger scale can tell us about the mechanics of the slave trade?

Correct. Radioisotope surveys are a powerful tool for archaeologists that's used for dating both human and material remains (e.g. obsidian/ceramic sources), but the global coverage is pretty low.
Thanks for the confirmation that I wasn't in the grips of a fever dream.

I'm still having trouble wrapping my head around the existence of a study that incorporates fields as distant as anthropology and nuclear physics.

For anyone looking into this, the field is (usually) called "organic geo-chemistry" and/or "paleo-isotope ecology"; the two fields are interwoven to get results like these, or the diet of early mammals. It's generally a collaboration between anthropologist and paleontologist.
The term "isotopic analysis" is a bit more specific to what's going on here. There are dedicated labs specializing in it that will do samples for (relatively) cheap, especially for the fancier methods. Paleontologists aren't necessarily any more skilled here than anthropologists/archaeologists. Those three are fairly similar roles with a lot of skill overlap that doesn't necessarily include analytical/nuclear chemistry stuff. The labs tend to be staffed by specialists from non-historical departments at the institution they're associated with in my experience.
It's actually a very common class of techniques. Carbon-14 dating relies on the ratios of carbon atoms, and is widely used for dating younger stuff. However, its relatively short half life means that for older stuff archeologists need to rely on other elements rarely found in organic materials like the uranium-lead decay path or in this case strontium.
Carbon dating is good up to 50kya, i.e. anything an archeologist is likely to be involved with. There's a separate issue dating things around 2500 BP called the Hallstatt plateau, but the slave trade this paper is looking at happened more recently than either of these (400 BP max). The problem is that carbon dating doesn't give you very good localization because it's generated by atmospheric sources. Strontium is almost exclusively of geological origin and the ratio varies a lot, so you can build a good map with it.
Really fascinating methods. Visiting the Slavery Museum in Luanda shows some of the origin pathways too. Interesting to compare the exhibits in the musuem in Angola with the (incredible) exhibits in the National Museum of African American History and Culture in Washington DC. Both approach the subject from opposite angles.
here in Coastal California we definitely hear about the historical topic as social stress rises generally.. given the museum exhibit in DC and the history of commercial slavery in North America.. it strikes me as profound that many (most?) of the active slave owners and traders in the USA were actually killed in a short time span, called the US Civil War. The anger and resentment and race hate culminating in literally shooting and killing on such a mass scale. The literal, physical brutality of entire cycle seems so distant in the modern time.

Since so much of the literate, conscious slave trade comes from societies of Central Asia (apparently also elements of Sweden and England, and of course the Portugese).. I was curious and asked an observant Muslim here about slavery.. he just looked calmly and replied "it was time for it to end" .. I got the feeling that the Muslim world had some kind of internal reckoning, and did (mostly) end the slavery trade at a certain time, similar time frame to the Civil War.

From the outside, not a specialist here.. it seems like the remaining modern slave trade is mostly driven by raw commerce.. like the fishing boats for example.. Zooming out, it seems like selling known-addictive drugs has similar drives..

Most people (including Muslims) have forgotten that the Muslim world used to capture and enslave large number of Christians on a regular basis.

In fact, it was one of the drivers of the Crusades, an idea conveniently forgotten by Muslims who point at the Crusades as evidence of the West's hostility to Muslims.

Enslaving others is, while not necessarily normal, not uncommon. The enlightenment really changed things around, which shows the power of ideas.

Nope, in the Muslim world slavery ended much later. Mostly halfway the 20th century. Mauretania was the last country to abolish slavery, in 1981. https://en.wikipedia.org/wiki/History_of_slavery_in_the_Musl...
got it - long read.. many new items for me there
There's still slavery, and I don't mean "modern day" or "Socratic" slavery. In Mauritania.

I'm sure Al Jazeera has a documentary.

I can testify that most of the enslavers did not perish during the Civil War - my great grandfather’s family - most likely from Angola/Congo and brought via Charleston - was enslaved in a small farm along the route taken by Sherman. His father was also the “slaveowner” and served in a small defense unit (equivalent of national guard). This is not a unique story, there are many Black families that managed to, for a time, hold onto land passed from those who enslaved them. Most of it was illegally taken back by 1900 - by the slaveowning families.
Where did you learn that most of the slave owners were killed in the war? Most of the South's slave owning political leadership including Robert E. Lee and Jefferson Davis lived long and healthy lives after the war.
". it strikes me as profound that many (most?) of the active slave owners and traders in the USA were actually killed in a short time span"

what is not clear about that question mark?

You have a very-colorful impression of the Civil War.
I'd be curious to know how stable these isotope ratios are over long periods of time. For example I could imagine as a river changes course and erodes different sediments, that would change the ratios for plants growing downstream. Likewise an increase in rainfall in an area might dilute the amount of groundwater it consumes.

I'd also be curious about patterns of human consumption. In the modern day, sea food is the primary source of strontium in people's diets, with dairy and meat products also being large contributors. Agricultural trade could easily lead to people eating animals raised in a different region which might have an outsized effect on a specific dietary mineral.