I agree ! inspecting a field with a pass at 100 feet would be seen as in accordance with normal aviation practice when landing at a falm strip.
The problems start when you don't like what you see and don't land, some might see this as low flying in as prohibited in rule 5 as it is not part of a landing.
I would be very suprized if the CAA took action in this case as they have burnt their fingers a number of times in court, I think that if they did look like taking action just a hint that the "flying lawyer" was going to defend you would be enough to make them think twice.