B. Understatement
For many sport, the Olympics is considered the top level of competition. If a coach's team wins the Olympics he is most likely considered one of the top coaches in the world. Merely stating that he is glad for the gold medal is an understatement because he is most likely more than just glad. He is probably thrilled, ecstatic, and excited.
A hyperbole is an over exaggeration. This is the opposite of what is happening with this statement from the coach. The coach is understating so much one might think he is being sarcastic, but this is an understatement. This is also not irony.