Even though the official website lists his "Introduction" song as an original, I believe that it is just a mistake on the web design. If you take a listen to his track, then compare it with this:
http://www.youtube.com/watch?v=PQDMxoFBjfw
You can see that it is in fact very similar. Adding the fact that the album is a Touhou arrangement and that estha has used that same track for introductions on other albums, I think it's very likely that Introduction is in fact meant to be an arrangement of that song.