Various theories are being advanced. Tsunami victims is one. Another is that the remains are from an aircrash or ship sinking. Given the way those yellow ducks have travelled the world's oceans the feet could have come from anywhere. One idea is that the feet have survived because of the trainers which have the usual cushion soles. These, it is said, contain lots of air bubbles which is why the feet have not sunk to the bottom of the oceans and been devoured with the rest of the bodies but have floated around near or on the surface until coming ashore.
I shall be interested to read the results of DNA tests etc which should establish many answers but as far as I am aware they Canadian authorities have not yet said if the feet are white, black, asian or whatever.