"Who were you expecting, the jolly green giant?" See, Peter, this is why he doesn't tell people the truth. It makes them act like they're not sure whether to kneel or flee. He's suddenly something Other, rather than just another (albeit super-powered) guy.

He debates with himself for a moment before deciding not to tell Peter that he's actually much, much larger when he's not in a human vessel. probably best to avoid the whole vessel thing entirely. "I chose to look like this, thanks." Technically true. He's glad that one worked.