"They're..." Papyrus begins, fumbles, and starts over. "Their parent is, really into underwater basket weaving?"

Maybe there's more clues in some of the other murals? He starts looking around for more imagery they've overlooked, because he's missing too much of the context to begin to feel truly confident in his sense of the narrative here.

Sure, he could go with the perfectly acceptable way of making one up and sticking to it regardless of contradictions from the rest of reality, a time-honored classic... But he's getting the sense like Angus would find some way to poke holes in that sort of theory. And he wants to help! And win Angus' respect!