A guy in the pet store told me that his Chihuahua is full grown now at 12 weeks. She weighs in at 3 lbs.True?

He told me that his Vet told him this. That his Chihuahua is actually a tea cup which I know there is no such thing just a runt being called that for more money. He told me that my dog was very nice though, she too being a Chihuahua at a year old weighing in at a healthy 4.5 lbs. Another lady at the pet store said my dog was big and that her neighbors' Chihuahuas were half the size as mine. Well I love my dog and I can't imagine her any smaller then she is. Any feed back on this? I guess these people hurt my feelings and kind of ticked me off at the same time.