Yes, cultural homogeneity is a myth. That being said, the premise of your article sets up a binary of "cultural homogeneity or heterogeneity" that is also a myth.
I emigrated to Austria 30 years ago. People often claim that Austria is very homogeneous and that is why (for example) social democracy works here. When I point out that 50% of Vienna is 1st or 2nd generation immigrants, the person making that claim fades into the shrubbery a la the Homer Simpson meme.
That is Vienna, not Austria in total. 25% of all Austrian residents live in VERY cosmopolitan Vienna. We also have Starbucks and (sadly) KFC and Burger King, etc. Outside of Vienna the culture of Austria is VERY different.
In Vienna you can get by on English. Your neighbors, if they are from Vienna (or immigrants) won't care. If your neighbors in Vienna are NOT from Vienna, they will.
If you live or work outside of Vienna, your neighbors and/or colleagues may care a lot about how you talk, what religion you are, who your partner is, etc. You can be asked (as I was) 10 years after living there, starting a business, being married to a local, and having a child, "When are you going to move home?"
The locals outside Vienna care a lot about their culture; their traditional dress; their traditional foods; their holidays; their history; e.g. their culture.
It is a minority that will talk to you openly like that. The looks you'll get, and the things you'll hear through the grapevine make it clear that "the locals" are concerned about how an Auslander (foreigner) affects their community.
I'd bet dollars to topfen golatschen that outside major cities it is similar in Japan.
I'm very lucky. Up until Bush invaded Iraq, American expats had the sun shining out of our asses here in Austria. Since 2003 we've gotten taken down quite a few pegs, but we're still way above anyone from the East.
My family comes from England and Germany, so if I don't open my mouth, no one knows I'm not a local. Once I got to know some locals here, it became clear that they like their culture - even if it is a constantly changing mix of other cultures - and they don't want it to change (or if so relatively little).
