Hi, new person!
I agree, in the absence of any real data, with Mr Jack: it's likely just a variant with no Deep Evolutionary Significance (TM). You might try "epicanthal fold" in Google, if you're really interested - that's the real name of the eyelid structure that gives rise to "slanted eyes." I didn't see much in the first page or two there apart from definitions and ads from cosmetic surgeons, though.