Many people including myself will wear swim trunks under my clothes if I know I am going out into the water. It's a lot easier than having to take all of your clothes off, including underwear, just to put on your swim trunks. It avoids having to get naked. Most people, including myself, will take off their outer clothes and leave them at the designated place on the shore line before going into the water. He was at a private residence, so whatever valuables he had in his pant packets were relatively safe from theft. This is not always so at a public beach though. This is my interpretation of his 'clothes were found separate from his body'.