I think there are two completely different questions, and we are talking about different ones:I don't know enough about each of these cases to comment, though I will say that imperial Japan certainly got explicitly racist ideas from Europe.
Generally, the degree of racialization going on in a particular example of ethnic strife can be known.
The historical origins of racism lie in early modern Europe, so that essay is an answer in a literal sense to the question "at what point does group bias become racism?"
I haven't read those essays in a while but the basic answer is a combination of a few different ideas was necessary to produce scientific racism. It is inextricably tied up in the development of rational science, the displacement of fundamentally religious worldviews particularly as it relates to humanity and humanity's place in the universe, and crucially the idea of "progress" which allowed Europeans to imagine they were more "advanced" than the other peoples they were encountering around the globe.
One is "historically, when did the modern understanding of "race", and the discrimination based upon that, come to be".
The other is "what class of things does the term racism encompass today". One could then ask "using that definition, what things in the past would we class as racism". If you are going to include the "othering" that resulted in the Rwandan genocide as racism today, and use the same definition to ask if the socio-ethnic caste system that predated western contact was racist I would have to say yes.