You seem to have sufficient reasons to reject the paper on its (de)merits, whether or not it was written by a bot.
You can certainly tell the editor that you are suspicious.
I doubt that the editor has software (free or otherwise) that could tell whether the paper was bot generated.
I wonder if the many citations are real. Chatbots are notably nonsensical in that realm. You could quickly check a few. Even if real they may be irrelevant.
Finally, LLMs can indeed scrape SE posts. Whether they could use that information to learn how to do better is unclear.
Edit in answer to comments from the OP.
Just describe the mess you found when you tried to check the references. You do not need to prove anything.
It will not reflect badly on you if the editor disagrees with you (though it may reflect badly on the editor).