The USA has people taking part in the World Naked Bike Rides and the Folsom Street Fair, but the USA has "norms against public nudity". The millions of people going outside each day are not naked or expecting to see others naked. That's a "norm" and it applies to Japan as well; clothed is normal, the exceptions are few and constrained to a few places/situations/events.

A photo of a Japanese public space, would you expect to see a) everyone clothed, b) everyone naked, c) roughly 50:50 as people choose for themselves and going naked is a perfectly acceptable thing to do which nobody thinks is weird ? (a), obviously.