A and C.
I presume that you are qualified as an engineer and must have seen some things during your working life that have raised concerns when you have inspected them? My thoughts are that this thread is not about "trial by Ppruners" as you suggest but one of common sense. I am sure you will agree that damage following an aircraft hitting a ground based object can often be hidden within a structure and not immediately obvious to a quick visual inspection.
John who witnessed the incident is an experienced rotary pilot and in my opinion did the responsible thing by informing ATC, he has also acted as a true gentleman by not embarrassing the pilot further in public by publishing the photographs or registration of the aircraft.
The pilots actions in continuing his flight does raise questions of his attitude to flight safety, and it has rightly been said on here a failure due to hidden damage may not occur immediately so it could become an issue to someone flying the aircraft at a later date.
Perhaps if I reflect on my own experiences of issues with aircraft through damage that was not blatantly obvious, it will help explain why on a personal note I feel quite strongly about the pilots attitude to the damage. Some twenty plus years ago I shared a hangar with a well known aerobatic pilot, he had a very casual approach to fear - for his day job he was a deep sea saturation diver... His style of aerobatics was to say the least aggressive. One day he asked my opinion about the top wing of his Pitts special - at face value it looked fine. However when you tapped the top of the dbox construction near the center it sounded dead and pushing it with your fingers showed a surprising about of deflection. I suggested that needed checking by an engineer. He took my advice, he did not fly that day and when I saw him two weeks later he bought me a beer!! He explained that the engineers had discovered that the wing had failed, the glue had separated from the wood and the wing was close to a catastrophic failure - all not visible by quick inspection. Brian sadly died some years later when an aircraft he was flying in the middle east suffered structural failure in flight. The cause was thought to be due to previous unseen (and uninspected) over stressing of its construction that led to an in flight failure.
If someone in a car has a bump, its not too life critical. if it fails - you can pull over and walk. If you bump a boat and there is unseen damage below the waterline you have a chance if you can swim. However in an aeroplane its hard to pull over in flight and even harder to try to fly on your own (I have not seen anyone with feathers who can fly).