Respected researchers giving imprecise or misleading explanations in casual conversations
There is nothing strange about this. Not everyone is good at translating the very technical problems they are working on, without advance preparation, on demand and at a moment’s notice, into a polished speech that a random person they encounter (mathematician or not) will find understandable. I think the correlation between what you observed and the quality of this person’s work is essentially zero.

As for the fact that you found his description “misleading” because his papers suggest he usually works on other topics: well, he may be trying to do new work in an area he hasn’t worked on before. This is often my situation, and my own answer when people ask me what I’m working on (especially if the question is posed in the present tense as in your description) will occasionally have little or nothing to do with anything I’ve published.