For him to confirm his claim that it is a specifically “western” thing to treat Japan so in news sources, he has to speak a variety of both “western" and “non western" languages to truly ascertain that trend.
He must both confirm that it happens in “western” news sources of many different countries, as well as that it doesn't happen in ”non western” news sources.
One would have to speak a considerable number of languages to claim sufficient expertise in world news reporting to make this claim.
I'm not sure as to how I'm supposed to challenge the challenge to my challenge without being “confrontational” as you call it and point out the faults with the argument.
This is a hard problem, and a difficult lesson to learn. I know it took me a while, and I'm still bad at it.
I find it helps to make your points, while trying to maintain a pleasant tone (Easier said than done, and I'm not a good person to teach this). I also find it helps to add questions asking for either other peoples opinions or clarifications on their position, as that helps show that you're not just talking, but also listening.
Edit: Also, the largest part for me at least is to remember that an attack on your argument is not a personal attack against you. I've had issues with doing this my whole life, and am still working on it.
I did not.
Only if one makes a claim about what is generally written in such books.