Well that was rude! Did you say something back??
If your Vet has never said anything to you, I wouldn't worry about it. Or if you are stressed about it make an apt to check with him... so you wont have to worry.
6 pounds sounds healthy to me!
Sometimes I worry Pnut is too skinny, I can feel his spine and hip bones.. but the Vet tells me he is healthy at 4 pounds. I think Yorkies, like us have different little bodies. That person apparently has no clue about Yorkies so don't let that get to you.