This is unfortunately not all that uncommon.
Authorities say a human foot in a running shoe has washed ashore on San Francisco’s Ocean Beach with no sign of the rest of the body.
12 feet were found in British Columbia since 2007. Some were identified as those who had jumped to their death from a bridge. Others may have fallen off boats. Foul play has not been ruled out but it’s hard to tell by just the feet that survive. Running shoes float so once the foot becomes unattached, that is what remains to return back to shore. Gruesome but has an explanation.
See this great discussion about the mystery of the severed feet.