normal cycling shoes have a cleat you lock into the pedal with that allow very little movement. sometimes just a few mm of position change is all it takes to relieve a nagging ache and im guessing he found it easier to get comfortable with a shoe he can move around on the pedal.

I've stopped mid ride to adjust my cleats just a smidge when i was feeling discomfort. you don't want to mess around with knee pain especially when riding 12 hours a day