Well, if it were a 2000 say 2.5RS that he turned into an sti, then that is something definitely special you don't see many of those around at all.
My assumtion is that he bought the 2.5 rs, then started modding it. Now when the STi came to the states in 2004, he decided that he would swap a USDM STi engine in.
Therefore, at the time he bought the car, the STI wasn't available to purchase yet.
Not trying to flame dude, just trying to get you to see what we are all talking about.
I believe a former member of this site (zooph) is going the same route with his 2.5rs? i forget.