Fundamentally, if the DoD is willing to pay a reservist to be recalled then the military duty is legit by definition.
The military loves volunteers, because it means one less involuntary recall, and those have political consequences (they are tracked in detail by the OSD).
One one hand I generally encourage folks to complete one year before taking a recall, just to avoid the appearance of gaming the system but either way it's legit.
Also involuntary recalls do happen, so in some cases it was not the pilot's plan at all.