That comment would bother me, too. She sounded very dismissive. Obviously your son has an excellent ability to focus on something that is advanced in it and of itself. It is not typical for 2.5 year old to sped any amount of time on puzzle and maze books.
If for some reason, she was only responding to the half of your remark regarding attention span of 2.5 year olds, she could just be interpreting that as meaning the time a 2.5 year old spends entertaining himself. But, IMO, a 2.5 year old playing at a train table for an hour is much different that a 2.5 year old solving puzzles for that long. I think you really need the qualifier.
In the end, It is probably fruitless to try to compare attention spans. My DD would not give a maze book a second look, but she would flip through an encyclopedia about the presidents for an hour.
DD(3) will play by herself for hours at a time inventing elaborate play scenarios with imaginary things. She will also sit and be read super long and complex books indefinitely. And, will sit and listen to anything you would want to teach her. Yet, she will get bored or frustrated with legos after 20 minutes, and will not focus on puzzles at all.
