Wet sand would have been recently cooled by water. It also experiences evaporative cooling.
Work Step by Step
Presumably the sand has been wetted recently by waves of cool ocean water washing over it. Water has a high heat capacity, so if a kg of water mixes with a kg of sand, the sand will cool more than the water warms. In other words, the wet beach sand is cooler than dry sand. There are also evaporative effects. Evaporation is a cooling process. As water evaporates from the wet sand, it cools its surroundings, including the sand itself.