I’m not sure it’s as much as that. He probably cannot lock the gate, but I imagine he could put up an “at your own risk” sign, that as long as he’s not got nails sticking up out of the pathway, should protect him from liability. I don’t think it’s really big encroachment on “property rights” to state that whatever public access was provided to the beach when you bought the land served as an encumbrance that continues past the purchase date.
He is actually locking the gate.