He quietly takes in the boy's words, and from what he can tell it seems he's grown fond of the other captives. That makes some sense. They are on the same side. He doesn't know if he understands how time can "stop" at home, but Diarmuid speaks as if he knows it to be true. He has no reason not to believe him.

The thought that he'll have yet more holes in his memory when he returns is particularly distressing, but he sets aside the thought as best he can for now, though his fists tense at his sides. He has to deal with one thing at a time, and right now that one thing is speaking to Diarmuid, who seems conflicted by the question. The soldier did not intend to make him confused.

"You don't have to answer."