As I read your initial post, he called the 10b, and called the pocket. He then “missed the 10b completely” hit the 15 and caromed the 10b. Aside from the fact that he might well have been playing the carom all along, he’s called the ball and pocket and made the ball in the pocket.
In terms of when to call it, the safest course is to call all banks, caroms and combos. In some rulesets (such as BCA) there is no such thing as an obvious combo. In others it might be possible that a combo is so obvious that it doesn’t need to be called, but I personally always call it to avoid any dispute.