True, but over time history gets distorted. We cant even be sure whether the numbers Caesar wrote about his armies were even true or just him boasting,and that was only 2000 years ago. We have barely any information of 48,000 BC. Now imagine that only in the infinite universe, where your entire race was pushed to the brink of annihilation (or actually annihilated in the case of the Equestrians). Facts are going to become blurred.

And anatomy likely wouldn't change much in 50,000 years. Humans have had a relatively unchanged physiology for well over 50,000 years