I was diagnosed at 15 but with noticeably severe symptoms.

I wouldn't worry about your son unless, as someone mentioned, it lasts. Otherwise, I would say he was just excited about his game. Also, I know Bipolar is not the greatest word to hear, but even the most distressful scenario is brighter in knowing your son will have something that most us never had. He will have a mom who both truly understands him and who truly does not judge him. He will have a mom who listens to him, attends to him, and is there for him when the world is not there for him. In short, he will have (has) a remarkable mom! It will be fine!