He probably could take that into court and have that action taken down.
However, I'm not so clear that third parties wouldn't capitalize upon the exclusivity he just de jure created by restricting land access. But without actual ownership of the beach itself to turn it into private property, he might have unintentionally triggered a tragedy of the commons scenario, where he's raised the attractiveness of that particular spot of the beach without being able to charge and throttle access for it, and those third parties will be able to deliver that access and charge for it, without having to pay for the beach capex and opex itself.
This has the potential to be environmentally terrible, and I'd rather truly not see that happen, even though if it does happen it would make others in this thread happy on how much a Pyrrhic victory it would represent for Khosla.