That is preference, as you can shoot with it folded to either side, and the only reason I can think of to have it fold right would be if you had a side rail with an optic mounted.
I prefer the right side folding because it balances better against your body when slung, but that is also preference; I do have a left side triangle folder AK, but it lacks a side rail optic mount.
It's not as easy to rack the charging handle with the stock folded right however, and you can't operate the safety.