If your going to offer your advice, you should look into what your saying before you say it. By saying it looks like tail rot, take him to the vet it could kill him is probably not the advice the OP was looking for, but you probably did give him a heart attack, so before you scare someone like that you should make sure it is indeed what your saying it is.
It could be a cricket bite, but even a minor injury or cricket bite can potentially get infected so definetly keep an eye on it and use the neosporin. You can also use diluted bentadine, until it looks like weak tea, and soak the end of his tail in that.