Every semi auto has the potential to MALFUNCTION and go full auto. There are multiple possible reasons.
Claiming the trigger "stuck" and it fired twice instead of once is generally something that can be determined by a competent forensic firearm technician in a lab exam of the gun.
It is, however, possible that some bit of something could have caused the firing pin to stick (resulting in a slamfire) and be dislodged in the process so the lab could not get the gun to reproduce the double fire.
MUCH more likely is that in the high stress of the situation, the shooter simply does not REMEMBER pulling the trigger a second time, and therefore believes he didn't and the only explanation he can come up with is "the trigger stuck".
If it is due to a mechanical flaw, the lab will find it. IF its due to something else, the lab MIGHT figure it out. If its due to the faulty memory of the shooter, the lab won't find anything wrong with the gun.