It makes sense to me that some aliens may appear exactly identical humans and not to each other, it should have been done more often, it's a potential "real" problem with dealing with other sophonts. They might know each other apart by scent, or voice pitch, or they may have some low level telepathy that identifies them that a human couldn't sense very easily, they are "aliens"
I hadnt thought about this before. Good point. I wish they had done this more often.