Don't feel bad, we've had members with full grown 3-pound Yorkies, who were told the same thing. Joey's around 5 1/2 pounds, and I was shopping with him when a lady came over to me, and remarked about how big he was. She informed me that she just got a brand new 10-week-old "teacup" yorkie who was 3 pounds.
Sometimes, I think people are just excited about their dogs and say stupid things.