It would be easily dismissed if said by someone much less accomplished. In this case, I just take it as a frank statement of belief.
Regardless, I think it's safe to say Minsky was a great intellect, of a caliber not often seen.
I would have preferred Asimov to say something like "Sagan and minsky are the brightest minds I've encountered in my life." And if you think Asimov is super smart, then you'll respect Sagan and Minsky that much more. And you'll respect Asimov too for not being so egotistical. It doesn't even matter if it's actually true or not.
Minsky, in my experience, demonstrated humility when talking with or listening to him. For that I gain admiration beyond the talent.