> Do they already know what meat is?

Yes, they do:

> "“Maybe they’re like the orfolei. You know, a carbon-based intelligence that goes through a meat stage.”"

What they cannot fathom is a sentient lifeform that achieves things but lives their entire lives as meat-based things, flapping their meat mouth parts to make disgusting meat sounds at each other. And I think they really never thought much about human reproduction!