The CFI stated to me that it happened so fast the light flashed grabbing his attention and he watched the temp rocket through 200 within the time it took to advise the Pilot in command
About the ONLY thing that can cause this kind of action is a preignition event, usually from a cracked ceramic on a spark plug. Or a tiny slim chance of a helicoil tang protruding into the head.
Jab heads do not have helicons (or they did not long ago) so a spark plug, most likely dropped caused this. Rough mechanics?