I don't know if this is the same one you read, but he basically said the same thing here:
http://www.en.barks.jp/news/?id=1000003853
"I hate to break it to fans of each my projects, whether it by KUROYUME, sads or solo, but in reality, it would often be the record company that would make the decision of which song should be released under which project. They would be like, “This song should be used for KUROYUME”. Of course, timing has a lot to do with it, but I don’t write my songs thinking, “This is for my solo; this is for KUROYUME”. Most of the songs on the album that I wrote were chosen like that. Then the offer to make a theme song for a movie came in. I wrote the song “Guernica” imagining a movie called “Bilocation”."