Here's a breakdown of Texas AP law.
It looks like he just filed a claim for title, claiming it was abandoned; the former owners now have three years to claim it and would definitely win a lawsuit. The three-year figure (rather than the ten under the catch-all statute) looks like it kicks in right now, since he's now got some form of enforceable deed, even if the original owners' claim is superior to his own. Had he not filed, he'd still be able to make an AP claim after the ten years were up. He seems pretty confident nobody will throw him out; I'm not as confident, but I'm sure he's done more research on the issue than I have, and after all, if he's right then the house would just sit there until the end of time anyway.
There is literally no reason for the neighbors to be mad at this dude other than simply not knowing that AP exists for exactly this reason, or racism.