Did he lie about his commitment being voluntary though?
If one is a Reservist prior to joining CX, you are obliged to disclose it and give details about when and where military duties are to take place. If subsequently called up to save goats from ISIS, CX still has to release said officer to those duties.
If he lied about it...or subsequently joined the reserves after joining CX, then thats down to him, and CX will resort to all kinds of goat****ery to impede his military duties.
Sounds like he has not helped his case though...