I'm pretty sure it's just a little patch of dried scales...like we can get patches of dried skin. Doesn't look like a typical burn, and I don't see how that part of him could get burned on a heat mat in any case. Keep an eye on the spot and it will likely disappear with the next shed, but another little patch like that could pop up somewhere else. I had a ball years ago that was prone to such little patches (just every once in a while, not all the time)...they're harmless and increasing humidity didn't seem to make any difference.