It's not "unfair treatment," it's perfectly normal for people to feel more comfortable around their own. They don't know if this guy knows train etiquette, if he has body odor - only around 10% of East Asians do, or maybe it's just that he's wider than the average Japanese person, as it appears so from his picture.
He's a guest in their country, and it's impudent for him to think he has the right to be sat next to at the same rate as Japanese people. If he doesn't like it, he should leave.
He's a guest in their country, and it's impudent for him to think he has the right to be sat next to at the same rate as Japanese people. If he doesn't like it, he should leave.