It is not usual but it is certainly not uncommon among many of the Slavic peoples - many of whom were overrun by the Mongols and also had centuries of contact with Tatars and other Asiatic peoples. It is also not uncommon in Finland, where the people have a mixed genetic heritage - roughly two thirds Caucasian and one third Asiatic. Then there has doubtless been some mixing between the Sami (and other polar peoples) and the larger populations in the southern parts of Scandinavia.

Personally I don't like the look, but it is only one small factor in whether I find a girl attractive. One of my favorite girls is a Japanese girl whose eyes almost look like slits - and it looks fine on her because it is her.