What's the difference with a pax who chooses to remove his shoes during the flight?
From a cabin crew point of view, the difference is that person had shoes on in the first place, and can be requested to put them on again for landing... as we all know, take off & landing are the two most critical phases of flight...
Congratulations to the Captain involved for having the guts to make the decision he felt was necessary at the time - after all, that is why he wears the 4 stripes.