> it just grabbed the vibe and built a whole arrangement around it.

I would also be very interested to know why and how this works. I usually upload the audio of my songs, and it immediately gets everything including harmonies, structure, melodies and lyrics, just amazing.

> not AI music as the finished product

I'm even amazed by music fully generated by AI (even when based on uploaded audio); with a bit of tweaking amazingly interesing music can be generated (see e.g. https://rochus-keller.ch/?p=1428).