I think people are misinterpreting the word "potentially" in this instance. I take it to mean that's what Thompson will be eligible for, not what the Rockets are projected to give him.
They've played hardball in extension talks with all of their recent premium young talent, no reason to think they'll stop at a tricky fitting player who hasn't developed in either area (still a non shooter without lead creator skills) necessary to become a star.
My guess is this young crop of complementary star/elite role player types, like Duren and him, will fall into a similar class as the more veteran Irving, Harden, Ingram and probably Young and Davis will, which is around $40 million AAV.