One hasn't resigned from the military unless the resignation
is accepted.
That would be quitting, an option not available in the military.
Not necessarily. I tendered my resignation to the Georgia Guard last December, but it wasn't accepted until February of this year. If my unit had been called up before my resignation was accepted, say in January, I'd still most assuredly be required to go play.
I think this guy is going to argue that his paperwork wasn't processed in a timely manner, (ie, it got lost, whatever), and that if it had, he would have been out.