It does appear to be a burn. Albeit a kind of first degree burn that hasn't really escalated to the tissue depths that we have seen previously. What makes me think that it's a burn is it's consistent with the history of using a heat mat w/o a thermostat. Even though it appears to be just a reddening of the scales what makes it more serious is the location of the burns. Seems to be near the vent and cloaca in one segment and then mid body in another. Certainly could be a concomitant scale rot as well. Imo, this will require a vet and medication not just betadine and neosporin. It may require silvadene and antibiotics to speed recovery and stave off any sepsis. Good luck and keep us updated.