as far a breaking any FAR's there are *no* regulations that specifically prohibit what he did.
Correct but they may get him on 61.13 Careless and reckless..
And AS WE ALL KNOW, "flight" ends when the skids touch down (according to the very same FAA)
That is for the purpose of "logging time", not for the purpose of who is responsible for the safe operation of the aircraft.
I happen to know that you CAN be violated for leaving the controls of an aircraft---even though it is done legally. In Hawaii, we would hot load and refuel every day. We would also get out and leave the controls unattended to check for "fuel levels, oil levels, seatbelts, headsets, etc"---these words were written into our FAA approved 135 manual. We were allowed to leave the "immediate vicinity" of the aircraft for "blue room" breaks when our trained ground crew would do a control hold.
I happen to know of a pilot..
who took a 10 day vacation based upon the FAA's definition of the word "etc". He was leaning on the door waiting for the "trained ground crew" after having checked "fuel levels, oil levels, seatbelts, headsets, etc", and was charged with FAR 61.13.