It doesn't look like a burn- there are plenty pictures of those on here. I've seen similar-looking injuries on dogs before, and for them that's a cut. Like "oops I slipped with the scissors while clipping knots". Obviously snakes don't have fur to knot, but if there's anything with sharp corners or ridges in his tank I'd recommend removing it.

Are you feeding him live? Is there anyone in the house that might have tried to feed him while you were out?

I'm pretty new at this myself so of course I'm no expert, it could very well be something else entirely. Either way I'd recommend a vet visit, that looks like it would be painful and easily re-injured.