True of course. I've seen estimates of about 10% (your link quotes 11%) of children (i.e., 90% of children don't have it) but the obvious question is on what basis what the diagnosis made? You can guarantee that only a few of those kids have had an MRI scan determining a brain structure indicative of a structural association with dyscalculia in the brain. Easy to jump to conclusions and miss many other possibilities which do not present apparently impassable barriers to learning maths.