Hrqls: In that game you wouldn't care about gammons. It's such an overwhelming loser that you'd drop it like a smelly dead cat and be grateful for your opponent's mistake.

Your opponent should have kept the prime and hit you as soon as possible in the hope of being hit as you come off the bar and, in turn, hitting your blot on 4, or otherwise picking up a companion for your trapped man. That would increase his gammon chances considerably. Even without hitting you, it is, as grenv said, too good to double.