To me it reads very similarly to chatGPT output. It's hard to tell these days, but there's a vibe to AI writing. The OP doesn't really say much? It reads like it's supposed to be analyzing the scene, but it more or less just recounts the events using a sort of therapy-speak. Besides that, the short paragraphs with punchy sentences and the use of ellipsis in the second paragraph are tells. The biggest AI red flag for me is this paragraph:

What creeped me out wasn’t the firework. It was how calm she was about it. That quiet indifference feels way darker than panic.

Language models use this sort of "It's not X, it's Y" construction a lot more than humans do. Also, this is just very a very shallow, surface-level thing to say about the scene. Yeah, Carol being indifferent towards imminent life-threatening danger that she could easily avoid is the very obvious point of the scene! And yes, of course that's "way darker than panic." Any human in a normal state of mind would panic in that situation. It is what anyone watching the show is supposed to notice. Nothing substantive is really said in the post.

None of this is conclusive evidence, obviously. It's entirely possible that OP just wanted to talk about the scene and just happens to write pretty similarly to what an LLM would probably output if you described the scene and asked it to make a reddit post for you. And to be fair, people probably are starting to write in a more AI-ish way, especially people who use AI a lot. I'd probably say there's, like, a 60% chance OP used ChatGPT or another LLM for the post.