But, y'know, for all his bluster here...I can really see that moment where Mias first sees them at the pool. They've probably been missing for a while, and he's been searching - probably getting more and more terrified the longer she's gone - until he breaks through some bushes or trees or something and sees her there. Just staring into the pool with Abernos. And he doesn't know how long she's been there, so how much has she forgotten? Does she even remember him? And it's just this moment of panic and terror that freezes him to the spot for a moment before he races over and scoops her up, and that fear doesn't go away until she starts yelling at him - but of course by this time his expression is once more schooled into that insufferable superiority, and he can yell at her without her ever realizing how much seeing her there shook him.
(Or he was just pissed she ignored him yet again and just flounced off with her, stupid girl.)