No doubt some of these parents were overrepresenting their kids, or being lax on the meaning of the word "sentence", but how do you know their kids were "barely saying a few words at that age". Pretty much every kid I know does way more in the comfort of their house than they do in public.
I agree. I do recall dd9's ped asking me if she was saying any words yet at around 12-18 months b/c she was totally silent at her dr apt. She had been speaking since 5 months and was a non stop chatterbox at home. That said, I am as certain as I can be in some of these instances that there is some significant overestimation going on. I don't believe that it is a result of malice but more parental insecurity and comparing their children to others who were somewhat delayed. Things like, "uh, uh, uh!" were interpreted as "sentences" the same as reading DRA level 8 books in 1st grade (exact # reported to me by the mom) was interpreted as "third grade level."
I'm really not a fan of gauging a child's LOG based on parental reports unless there is significant data to support this (and not just a child who reads above grade level).
