Spelling Mistake, Or Dumb?

In the quest Wrath of the Mummy, Achper says,

"If I know Mummies?"

This doesn't grammar correctly even if it was right, but I'm probably just dumb, so please tell me why.

 

My guess is that it's a contextual response to an unstated player question (e.g. "<NPC> sent me here, do you know [about] mummies"?). But you're right that the ommited "about" is a little awkward with a plural noun (as opposed to the case of "plural" nouns that are actually singular).