50 Cal strafing an armored GV will not blow it up.
99.9% chance that this is what happened --- you took out his gun, and he ended the sortie. As I recall, when you choose to end a sortie when a kill is awarded (rather than being killed outright), those who are left behind are shown an exploding GV animation. This is much less weird than having it simply disappear, which would be the other approach.