I mean, I agree that he needs a lot more evidence to be convincing but that doesn't necessarily mean he's a shill. Just say his claims are unfounded and move on. If you look at the rest of his post history it looks fairly innocuous.

You should take everything with a grain of salt, regardless of whether someone posts a lot on a site or not. Use your own judgment. People could just be spouting off things they think are true. I've seen plenty of that with established and new posters alike who say things that are more 'boomer' than 'shill'.