Molly looks very much like a girl to me, but maybe because I have been looking at Yorkie pictures long enough that I can usually tell by the face.
Don't worry about it! Everyone thinks Teddy is a girl, despite all of the boy colors he wears.
Often it has more to do with what the person is accustomed to. Many people have had only male dogs or only female dogs. I grew up with only female dogs and knew very few people with males.