Yeah, no. They look at the character with their eyeballs, and notice western features. Simply noticing that some Anime characters look more western than eastern doesn't require years of nerding out on Anime. It's very basic visual identification.
Now, if Scarjo, or some other American got the role for this character in a movie, it would be a bit more glaring as she would look look nothing like it, and the facial features are decisively eastern looking:
And again, I'm not arguing that Major
is a westerner, just that visually she looks more like a westerner, and it made sense to cast a westerner that shared the same basic features. Besides, she's a fantastical cyborg with an artificial body. It's not exactly like casting John Wayne as Genghis Khan, as some would like to believe.