Sounds serious regardless of what happened. I'd find a rotary specialist and have him check it out. If that other mechanic is at fault, he owes you big. And the only way you can know if he is and get the proof necessary to get what he owes you is to get another pro to look at the engine.

 

Could've been something in the intake...a nut or bolt could have slid down the intake manifold and basically came to rest in the lowest runner where it meets the iron. As the engine ran the pulses of the rotor pulled and pushed it and eventually it made its way into the port and chamber. They can run several hours this way, I have seen it before.