Well, that's frustrating. I guess if it turns out to be a one time occurrence, it is more likely a bite. If he starts getting more spots, then it seems like it could be his food. Sounds like only time will tell for certain.
Does he take Advantix? I've got little Zulee on it because it deters mosquitos, biting flies, ticks, lice and fleas.
Sounds like Harry is on his way to getting all better.