people telling me singers I mentioned not being able to participate in certain music comps or charts because they were from certain places.
That's not what was said at all. Plus, it was just the set up to a line about Rowling, so I needed to mention both J and K.
So maybe stop getting your knickers in a twist over a random post that was factually accurate - J-Pop and K-Pop both exist, but whether acts involved from either country (or elsewhere) are popular in either or both is another matter - and wasn't aimed at correcting you.
Also, just saying XJ' would have been a funnier line in your original post anyway as J and G are phonetically similar which plays well within comedy, although I would have then had to forgo my own effort at humour (or what passes for it on RAWK).