Thanks for the reply!
It's wood burning...
Yeah, I'm thinking it's a solid piece of wood that runs part way up the wall. It's weird because the tv mount is mounted on studs. But according to the stud finder, the studs stop a bit beneath the mount. I assumed they were being connected by a horizontal stud. But maybe they're connected to this solid piece of wood.
I'm not sure if I should try cutting out the piece of wood or cutting a new hole higher up. I'm afraid that if I cut the wood out, there won't be enough room to fish the cables horizontally. But if I cut another hole higher, then I have to patch the drywall anyway, so I may as well rip out more drywall haha. Thoughts?