Well, that would depend. If he claimed to be an alien, Dib would be inclined to believe him. The same went for a sentient artifical intelligents. Dib might even believe he's a ghost. Weirder things have happened.

"Try me," Dib said, powering down his laptop and hopping off the retaining wall. Standing, he only came up to Lucifer's stomach or thereabouts, so he wasn't exactly an imposing figure. But he tried anyway.