Japan is definitely more insular than Korea, but keep in mind that whenever you see a "weird Japan" story on the internet, it's probably "weird in Japan" too. Tokyo has such a large number of people living in such close proximity that it enables the birth of some very weird subcultures, but these people are most definitely not taken seriously by your average Japanese person.

Compare this to a story I saw on AC360 the other day - there's a salon in San Francisco that rejuvenates your skin by punching and slapping you. Imagine a Japanese person reading about that and thinking "wow, Americans are so weird!" That's the same position you're in with that donut head thing.