"I mean, everyone is dumb compared to you."

Getting close to Senku levels of smarts is a very, very high bar to aim for, okay. It's not like Inigo thinks he's anything but dumb to the guy, especially since Inigo doesn't think he even hits average standards of intelligence, let alone anything higher than that or even close to where Senku is..

"So I don't see it as an insult as much as a.. description when you're the one saying it." That clearly makes sense. In Inigo's head. "Besides, everything else you're saying about him doesn't sound so bad!"