Bumping a well behaving passenger in preference of a "more important" one doesn't really fall into either category.
Considering the passenger in this story has already consulted legal counsil, I'm thinking the lawyer agrees that he did nothing wrong.
https://www.justice.gov/usam/criminal-resource-manual-1411-i...
There's a lot of room in between a contractual dispute and interference.
It applies only in the "Special Aircraft Jurisdiction of the United States":
"An individual on an aircraft in the special aircraft jurisdiction of the United States who, by assaulting or intimidating a flight crew member or flight attendant of the aircraft, interferes with the performance of the duties of the member or attendant..." [1]
An aircraft is in the special aircraft jurisdiction of the United States only while the aircraft is "in flight." [2]
"An aircraft is "in flight" from the moment when all external doors are closed following embarkation until the moment when one such door is opened for disembarkation, or in the case of a forced landing, until competent authorities take responsibility for the aircraft"
IANAL, but it would seem difficult to charge anyone with "interfering with a flight crew" if the door hasn't been shut. The language doesn't seem ambiguous.
[1] https://www.gpo.gov/fdsys/pkg/USCODE-2009-title49/html/USCOD... (scroll down to the 46504 section)
[2] https://www.justice.gov/usam/criminal-resource-manual-1405-s...