I did not find the word "belief" in that TSI regulation.
In the US there is a standard approach called "void for vagueness" which means that a law or regulation cannot be decided by a typical person cannot be used. For example, laws about debris on lawns. Since a single leaf clipping from a grass blade is "debris" would a typical person decide to fine the offending homeowner over that? So they get badly drafted laws overturned on that basis.
In this case both the "belief" argument and standard of proof in the regulation are severely lacking. The regulation certainly implies the responsibility is on having direct and certain knowledge of the event's occurrence, which your hypothetical owner doesn't have.
The owner can certainly ground or scrap their own aircraft if they feel it is unsafe to operate. They can also refuse to allow access to the aircraft for that person. And it looks like they can go with their gut and report their belief. I presume they can also be sued for making a false accusation if there is no other proof of the event having happened.
But all of this is moot until a court rules on it, so you need to gain access to precedent cases to be sure or be willing to push a case through to a decision.
Best of luck with BLK. (Basic Legal Knowledge)