What initially made me think scale-rot rather than burn is the placement of the irritation. Burns usually seem most severe either in the middle of the belly scales, or they cover the whole scale. Here it looks like the irritation is mainly located in the crevices between scales which is where bacteria are more prone to hang out. Unless there is blistering in between how would a burn damage only the bits furthest away from the heat source (the cracks between scales)?

That being said, I have plenty experience spotting and walking someone through scale-rot but very little experience spotting burns unless they're really obvious, so I could easily be mistaken that this is a burn.