It's really telling that you are a good keeper, when you aren't afraid to admit that there were unintentional husbandry issues and that you are endeavoring to remedy things. There are learning curves with keeping living things and no one is perfect.
I applaud you for seeking help, following through, and being willing to accept constructive criticism, without taking it personally. We are all here to help and some of us may have more tact than others, but in the end, we only hope to see these animals live the best lives possible.
I will add that renal disease often coincides with edema and I agree with other's observation that there is edema present, behind the casque, at a minimum. It is nothing to worry about, as the vet's findings already explain it. Increasing his oppetunities to drink, including placing him in a shower, outside of his cage, may help flush his system and he should be offered as much water as he can get, while on medications. I'd still avoid prolonged periods of wetness, I the enclosure, especially, with that abrasion still healing.
Best of luck to you both.