2009 Hyundai Sonata, Mysterious Death!!

I have an automatic, 2009 Hyundai Sonata. Up until recently it has been very dependable and no major issues or symptoms of such. Sunday, In one of those worst case scenarios, of how not to be prepared for the worst case scenarios, we were stranded in the mountains, no phone service, during a snow storm. Obviously all is well with the humans in this story. However, my car still remains in a comatose state. The moments leading up to this did not indicate any trouble, until my husband while using the manual shift option, may have in error down shifted when he meant to up-shift (we disagree on the exactness of details), from 4 to 3rd. The car and rpms revved, decreased speed suddenly, he felt or heard a pop of some sort in the. Then the engine died, and would not restart. It cranks but does not turn over. We had it towed to a shop. They have run diagnostics, tested compression, and more. They are unable to identify what happened and or why it won’t start. Is there something connected to the gear shift handle/transmission/engine relationship that could cause is to stop running and not start. Any and all theories / suggestions are welcome. Is this the first time this has happened? Also what is the etiquette for bringing these suggestions up to the mechanic shop? I don’t want to come off as the customer that knows zilch about cars, telling the experts, the internet says a, b, c. Thank you for your help!