Oh, I got ya...No, that's not at all "Mouth Rot"; Mouth Rot is an infection that can be on the outside of their mouth/lip but is typically also inside their mouths, and it's an infections that keeps aggressively spreading, killing all of the healthy tissue along it's way, and that is indicated by "necrotic" or dead tissue, which is very dark/black in color...So no worry about him in this respect.
Quite a lot of Dragons get that little area of built-up skin right on the end of their snout/tip of their mouths, it's almost like a little callous of built-up, dead skin. Sometimes it actually sheds off during their next shed, sometimes it just stays there. Typically it's caused by them rubbing their snout on something, like the glass of the tank, the floor of the tank, a rock or piece of decor, etc. A lot of Dragons that "Glass-Surf" quite a bit get this.
It may come off with his next regular shed of the area, it may not. I don't see any open wound in the area, or any dark or black tissue/skin around it, so that's good, but the best thing you can try to help it shed off and to keep it from getting infected is to buy a jar of Raw, Unpasteurized Honey (not regular honey, won't work), as it's a very strong, natural anti-microbial, and if you apply it once a day with a Q-Tip it will get rid of any infection/heal any open wound. Just don't leave any live insects inside his tank, they'll be attracted to the honey. The other thing you can try is getting some Raw, Unrefined Coconut Oil and applying it to the area at least once a day, kind of rub it in to the callous area. This works wonders in getting rid of Retained Shed, which is pretty much the same thing as what these callouses are. The Raw, Unrefined Coconut Oil applied once a day will re-
hydrate the built-up, dead skin and then help it to peel off. I use the Coconut Oil on any patch of Retained Shed any of my guys gets and within a week it's gone.