I suspect you're exactly right. I actually wish he would've said why the sandals specifically helped him because my immediate reaction was also, "what?"
In an interview with Sporza he said on day 1 he had knee issues because his cleat slipped. On day 2 he rode through the pain. On day 3 he wore sandals on his trip to a shop and noticed his knee didn’t hurt. So he bought flat pedals and continued on those using the sandals.
He also said the shop did not let him buy only the pedals so he bought the whole bike just for the pedals.
He also said the shop did not let him buy only the pedals so he bought the whole bike just for the pedals.