Blimey! firstly it was rather rude at a childrens party, and didn't give you much chance to respond! secondly, it does sound rather like she was trying to 'big' her own child up. Some parents do that, for whatever reason
Have the school/nursery raised any concerns? how well does she know your child? FWIW he sounds like a normal 4 yr old boy to me -- and from what you have said, he can concentrate, focus etc. I would also want her to expand on it - but going by what you have said, she might have an agenda....
As an aside, Ds1 was very verbal, but chose when and how he said things - he was very observant, and could sit for hours in his pushchair, not saying owt, but taking stuff in.
One day, we were in the park (he was about 18-24 months old - can't quite remember) we went down to the duck pond, and were joined by another mum and her similar age ds.
Both boys are busy feeding the ducks. Other boy was remarking on the ducks "loook duck - he likes bread!" he was very sweet, and I was chatting to him. My ds stood there listening, but silent.
After a while, the other mum asked me if ds was talking yet. I told her that he was, but he chose his moments - he was more of a silent observer, until he felt he could contribute.. She nodded sympathetically, and said she was a teacher, and started to make encouraging noises about speech therapy. she was very lovely and meaning well however.
As we were about to leave, her wee man said "Bye bye duckies!"
My son turned to him, and said "Actually, I think they are mallards, and that ones a moorhen..."
I just pissed myself. he's 15 now - and he's still reserved, with the odd ascerbic comment!