"That's not stupid at all. You made a reasonable assumption based on the information you had at the time. We all do that."

He doesn't sound like he's just saying that, he agrees fully with Nai. Vash wasn't even remotely stupid. Just hopeful. He could understand it. They had their own kin to return to.

"I'm glad in a way I have no choice about it.. I don't want to think about having to choose between my brother and Tessla." If he went home, what would happen to her? If he wasn't here now, how would that even affect these two? Would Vash wander the desert hoping to stumble across her again?

For a moment it seems like he intended to continue, but doesn't, falling silent instead. This was not ideal, but part of him was traitorously happy in spite of it. Here he still has family.