Well, I do not think Japanese pop culture is actually strange at all. It is just a meme that has somehow taken deep root, based on the supposed `otherness` of Japan in many Anglophone countries. So, when people see Pamyu Pamyu being weird, they say `Japan is strange!`, but when they see Lady Gaga wearing a meat dress, they say `Lady Gaga is strange`. Therefore, I think quite a number of countries could have had this meme applied to them. I would say we need three things:
1.) the country is rich enough and populous enough to develop a large native pop culture industry
2.) the country is connected into the global economy enough that its pop culture can easily spread
3.) average people in the `West` are woefully ignorant of that culture
The last is crucial. If, say, a Canadian acted as strangely as Lady Gaga or Pamyu Pamyu, people would only think of that individual as strange. They have some idea of what Canadian pop culture, or culture generally, is like, so they would not assume the weird person is representative of it. However, if the strangely acting person was from Ethiopia, or Korea, or even, to a lesser extent, Germany, people would be more willing to believe that the person in question was acting `normally` by the lights of their culture, as the people have no idea what the culture in question is really like.
By and large, I think Japan in OTL got stuck with this stereotype because for decades it was the only truly wealthy developed country that was not `Western`. Any other country reaching the same level of prosperity and as globally interconnected would probably suffer the same fate.
