He already said what happened to it! It's just not the full story, but it wasn't a lie! There's a muttered 'ow' with no actual pain attached to it when swatted, it didn't have to hurt for it to be an ow. "It's not stupid, okay? It isn't. It's just.. more complicated than just wanting something. Sometimes even if you want something you don't deserve it, and stealing it isn't always the right thing either.."

Stealing is sometimes fine, apparently. "And besides if she yells for you I won't know it's not me and I'll answer instead, it'll be weird." It is in fact, entirely excuses, and it's pretty obvious, but he can at least sulk about it in the shadow of the abandoned wagon. A good place for smaller!Vash to eat his noodles too.