Being considered prey is nothing new to Armin, so it's the natural way to identify the situation. He's unaware, upside down and backward as he happens to be at the moment that he's said something so disconcerting to Mika.

Rather, he's relieved to hear the response. It's more of a confirmation than surprise at this point, honestly. If Mika happens to be a monster, then that's how it is, a happenstance. Certainly, it isn't because that's the essence of Mika himself. If it is, Armin has seen absolutely nothing to suggest it so far.

He finds himself relaxing, even in a situation like this and during such an awful conversation. "Then I'm sorry about before."