Outing myself as a Bloodymary fan to say this but I don’t think Simon would believe Grace is an angel. Like I can picture, for a split second, that the thought crosses his mind but it’s only because… actually let me set the scene.
So. Simon is pulled from the SM-13 and either ends up on the Hail Mary or in the Bio-dome on Erid (don’t ask me how, I’m not sure) and he wakes up from either a medically induced coma or just his own unconsciousness, and there is a… man? Is that a man, standing over him? And he’s 1) hopped on the MOST pain relief he’s ever felt so he’s not even feeling scared and 2) Grace is stood in front of a light. Now point 2 is important because when you stand in front of a light beaming directly into the back of your head you get a corona like a total eclipse. This would, in theory, look like a halo! Now add Halo to mind numbing drugs and Grace saying “it’s okay don’t be scared” I can see Simon go “weird, no fucking way that’s a real angel.”
And then Grace moves to get a better look at Simon’s injuries and the halo is gone and Si’s like “oh yeah no I was right this is just some dude… wait.” (Cue freeze response as he realised that he’s not in pain which means he’s been drugged and he has no way to know if Grace is COI or HOW even got out of the Iron Lung when he’s pretty sure he got eaten by the eel and OH FUCK THE BLACK BOX?!? They’re gonna send him back down to get it aren’t they!? FUCK!) also I’m a firm believer that Simon would NOT immediately jump to violence first time he sees Grace.
Anyway shit gets sorted and it’s a few years later and they’re watching a movie in their cottage, when the topic of angels gets brought up. Simon tells Grace that he thought he was an angel for a microsecond because of the drugs and the halo and Grace is incredibly embarrassed that the first words out of his mouth were a rehash of Be Not Afraid.
It becomes a running joke but Simon is 100% aware that Grace is not some divine being and has never seriously been under the assumption that he was.
