In contrast, the present eastern boundary of Europe partially adheres to the Ural and Caucasus Mountains, which is somewhat arbitrary and inconsistent compared to any clear-cut definition of the term “continent”.
The current division of Eurasia into two continents now reflects East-West cultural, linguistic and ethnic differences which vary on a spectrum rather than with a sharp dividing line.
There’s really no physical reasoning for it. You can read on in that article for the historical basis if you want (basically, Homer and other Greeks coined it, and it just kind of stuck), but it’s really quite arbitrary where they actually draw the line.