It's a lot to take in. And while it is real instead of just being an elaborate psychotic break (albeit, a sort of 'real' that doesn't rule out everything being something generated in a holodeck), that's also not something that is easily proven. To say nothing of the fact that he's still not aware of the fact that Seifer is even so much as considering that particular possibility, or at least not until he catches the comment Seifer mutters to himself.

"The individuals presumably responsible for us being here in the first place."

And possibly also the various remnants of technology left behind, few and comparatively recently discovered though they might be, But that is something that's still uncertain, and besides, he figures that Seifer likely has enough on his plate to deal with as it is, to judge by his comments thus far.