Sorry to drag this one out of obscurity, but I have been away and missed it.
There is actually a marked helipad in the picnic area as described - nice round white circle and all.
I have landed there many times, but mostly on Water Board work or for the Blue Suit Aviation Company (the aforementioned wallopers.) Never raised an eyebrow before, but that was well before 11/9 .
If the angry people have a rego, it should be fairly simple to trace the driver, via CASA or the flying school which owns it.