That doesn't really make sense to me. As an outside observer, the #japanese tag seems like something that's perfectly suitable for this post as it talks about the Janapanese language in English and the actual word "Japanese" is in fact in English.
It would have been much better and less confusing if the content that was in Japanese was tagged with #jp much like the conetent in Korean tends to get tagged with #kr. I think that's a better system and would allow for people to tag their posts meaningfully as this post is not really about Japan but exactly about the language.
Of course, people are not going to change their behaviors just because I want to be pedantic about it, but still felt like sharing my two unsolicited cents on the matter.