I've been to China numerous times, my Mandarin sucks, I stand out, and I went wherever I wanted. Didn't try to go to Xinjiang, admittedly.
There's paperwork that says you have to check in with local authorities wherever you go, tell them what hotel you're staying at, and all this other stuff, but nobody actually does it. If you caused trouble, it'd probably be held against you after the fact is all.
There's no reason to assume this guy is some kind of agent because he had freedom of motion. He probably liked all the people he met, sees lots of ignorant anti-China commentary on the English internet, and is pushing back (perhaps too strongly).