This is about a condition called Persistent Median Artery or PMA, and it's a bit of a rabbit hole. Evidently having this condition is associated with increasing your odds or the impact of carpal tunnel syndrome.

PMA can manifest in a few different configurations, like depth to which it extends in the hand, thickness, etc. Here's an interesting read with pictures of dissected forearms showing PMA variants. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6327784/