All beaches in Costa Rica are public. People can walk up and down the beach as far as they would like, and there are plenty of places to get access to the beach. This is not like some places in Europe where beachfront hotels have roped off areas of the beach where only their guests can stay and the public cannot enjoy the same beach.
The white wall that lines the beach in this area is the dividing line between the public beach and the Diria Resort grounds. There is an entrance to the resort grounds where the little thatched roof gateway is located, and a guard there limits entrance to the resort grounds to those who are staying at the Diria Hotel or condos. Guests can enjoy the shade of the palm trees in the grassy area along the beach. They also do massages under the palm trees along the beach.
As is evident from the other photos shown in this series of photos from the gyrocopter ride that my son took, it was, unfortunately, a cloudy day when he did his gyrocopter ride. It was also low tide, and in the morning. A sunny afternoon would produce a scene with more people enjoying the beach, although it would still not be crowded by the standards of beaches in the USA or Europe.