I am saddened by this story. It reminds me of a similar accident.
I lost a friend, who was practicing for the Single-handed Farralons race out of San Francisco in 1981. Grover was sailing his J-24 which was found washed up on the beach south of San Francisco.
He probably fell overboard while relieving himself over the transom, and watched his perfectly trimmed boat sail away.......
These tragedies are all too easy to avoid with the use of a harness. To sail single handed and not tied-in is about the same as climbing a cliff without any protection or partner.
Just how hard is it to secure yourself to your boat? When sailing single-handed, choose to remain on-board, and tie in.