Your point about strict liability is a stark one in the circumstances of 'low flying'. It's a strict liability offence. A diligent pilot operating a serviceable aircraft can inadvertently breach the minimum height rules and it's still an offence. Easy example: VFR aircraft with an altimeter that 'overreads' by 50' and everything else is 'perfect and accurate' including the QNH. Cruising at 500' 'indicated' over the sea is actually only 450'. Strict liability offence.
This could be considered ‘an honest and reasonable mistake of fact’, and would be grounds for a successful defence, even in a strict liability matter.