Haven't gotten that specific comment, but some family members have sort of commented that small dogs can't be trained, don't know anything etc. Like when Pixie showed off her high five to a visitor, she commented "I guess that's all she knows?" It feels extra good to have them both trained to a high level of obedience, and they know loads of tricks and basic agility. One time we were out walking Pixie was walking off leash about 20 metres ahead of me, and we approached a dirt road that's normally really quiet, but this one time there was a car coming so I told Pixie to "wait" and she sat on the spot and didn't move a muscle until I caught up and released her. The people in the car stopped at a picnic area nearby and by that time were pointing and talking among themselves. When we came back the same way they started pointing and talking again. And other times we've passed people on the path who have kids and the dogs completely ignore them and just keep sniffing the path, that usually gets comments too, because it's very unusual for a dog to not lunge at everyone/everything here.
My dogs are usually the best behaved and most focused in any training class we go to as well, which is extra fun because they're small and no one expects small dogs to be trained.