That is officially not great acting skills. Maybe not as terrible as they could be, possibly enhanced by the fact that the Soldier is still, despite everything, a little nervous about Aziraphale in general. (Someone who tries that hard to be nice, they've gotta be hiding something. You know he aint. No, we don't know.)

It's not enough, though. They look back at him, torn between embarrassment and frustration. "What is." Maybe if they prompt, he'll find something to actually be angry about, and it will work enough that they can get an idea of how to deal with it?