The article spells it out pretty clearly. He made a commitment to the Navy and is now trying to get out of it.
My understanding is there is an exception policy in place for athletes with a legit chance to play in a pro league, and the armed forces have allowed deferment of service obligation in those cases. And, according to this kid, they told him he would have a chance to defer.
Athletes have a shelf life. Football shelf life is very short, and generally even shorter for guys who defy the odds and make it from a non-major conference school. If you are going to have an exemption policy, and you represent to athletes (as an incentive to have them attend one of the military academies) that they will have the chance to defer service, then best to let them do it when they make the cut at a pro team.