If it's light blood, that suggests its fresh and not dried. It could be a fissure (a small tear in the skin) which heals and gets re-torn periodically. Very common, but he MUST see a doctor to allay his fears and to make sure it is nothing more serious.
if it's very red (and not darker) I think it's more likely to be piles or some kind of small tear, but it's the sort of thing that needs checking with his gp.