Looking for an explanation of the Bastille scene.

Hey everyone! I’m wondering if someone could help explain a scene/line to me? I love Good Omens but have found it a bit hard to understand certain scenes as I am autistic and often have a hard time understanding certain social cues/ emotional reactions. This coupled with the fact that since I’m not British there may be cultural/societal norms that I don’t pick up on as it’s different from where I live.

To get on with it, there’s the scene where Aziraphale is trapped in the French prison when he goes to get crepes in Paris. He’s headed for the Bastille but is saved last minute by Crowley. I understand why he’s there but when Crowley eventually emerges and says the line: “Animals don’t kill each other with clever machines angel, only humans do that” Aziraphale initially reacts with a smile as his eyes widen and he goes “Crowley!” but when he turns around, sees Crowley and his faces seems to sour and he says “oh good lord” in an almost exasperated way while looking Crowley up and down. I have a really really hard time with this scene cause I don’t understand Aziraphale’s reaction. I assumed he was happy to see Crowley but the later part makes me think he wasn’t?

I have watched this scene at least a few times trying to read it but just can’t seem to know why he has that reaction. I’ve had trouble with other scenes in the past but I’ve looked some of them up on here and have found explanations but I haven’t found one for this scene. Any help in breaking it down would be much appreciated! There’s some amazing people on here with a real knack for breaking down scenes and body language etc and I’d love any and all interpretations! Thanks in advance! <3