I've seen him post stuff that I saw on other websites like Reddit before they were on imgflip. For example, remember this meme?
imgflip.com/i/2c64bt
I had seen people saying that EXACT thing (minus the raptor) on r/showerthoughts multiple times way before that meme was submitted.
He probably doesn't always steal from Reddit though, and I'm not judging him for it, when you think about it it's a good thing because that stuff is hilarious and more people get to see it.