The GOOD news is that even if it opened, there is a timed mechanical safety feature that ensures that by the time the bolt had been rotated and unlocked the time lapse ensures that the bullet will have left the rifle and be well on its way down range. But it still indicates a fault with the rifle. That it only happened once is puzzling. In any case, if the bolt and cocking piece is/are in serviceable condition the rifle will not fire unless the bolt is fully locked

Knowing all this, I'd take it out and have someone photograph you shoot it using a high speed camera equipped computer