I don't think we can say he was a groyper, but I think it's telling that Krash Patel has had the full force of the FBI behind the extremely partisan leftist claim and nothing has linked him to any leftist movements (yet).
I believe the Gov of Utah did actually hear people telling him that Robinson had succumbed to leftist ideology, but those people are shellshocked mormons trying to make sense of something that clearly wasn't expected in the slightest.
I think when the dust settles, we'll find Robinson was a textbook lone wolf who had a very personal hatred for Charlie Kirk, and all the while people will say that's clutching at straws - because I'm absolutely certain the partisan investigation will continue to try and create a link, any link, a meme-level link if necessary, to make this more political than it actually is.
Then again, let's consider it could easily be culture war bait and they already have the links they're claiming they don't have. Never underestimate how important it is to rub people's face in something they had absolutely nothing to do with.