Sarcastic, and brimming with the emotionalism of youth.
The mother doesn't have to call the child during school hours. In fact, most deployed parents and spouses do not call their relatives during school hours.
Maybe that's why the kid was so emotional? Maybe he figured if she was calling that time of day, something must be really really wrong.
Of course, if something is really really wrong, you don't get a call. The car pulls up in your driveway instead.
But, being ex-military, you know that.
Actually, I'm current military. It's no surprise that you wouldn't count the Reserves as military.