This is kind of funny/bizarre. And only one real reason why it could happen only in Japan: the tradition of taking your shoes off at the door even at schools.
This was when I was teaching at junior high. As I was leaving for the day, one girl was opening all the doors of the teacher's shoe locker, taking out the shoes and sniffing them. At first I thought she was cleaning the lockers cause they sometimes do that, but I asked her what she was doing and she unabashedly told me that all she was doing was sniffing them to see who had stinky shoes and who didn't. And she was approaching my shoe locker. Then she remarked that my shoes must be stinkiest of all!
Kind of annoying that. But, I have to admit that while there are certainly poor reasons to make such an assumption, such as racism and just disliking someone, there are good reasons also, such as noting the fact that in western countries we don't remove our shoes so much or in public, so some people really don't care about the state of their feet, their socks, or their shoes, and yes, I have run into some Americans who seem to have not removed their shoes or changed their socks or washed their feet for a month, and I had the bad luck to be around when they finally took off their shoes. JESUS! Still, I could not help but feel a little offended.
Anyway, she gets to my locker, takes out my shoes, and she could not smell anything all. Of all the shoes, only mine had no smell. And they were old shoes too, or they would have at least smelled like new shoes. Nope. Nothing. Man was she surprised! And then I could not help but feel a little proud!
Thing is, my feet do not sweat nor do they produce any oil. My feet are so dry, the skin is a bit cracked. But no smell.
So now she will probably go on thinking that gaijin feet don't smell....until one day....she will get a BIG surprise!