It's not really debatable, because it was written by someone who was in Dream Theater at the time, performed by three, likely four musicians who were members of Dream Theater at the time (Kevin, James, Mike, and likely John), and, most importantly, the CD on which it was released says "Dream Theater" on the cover and the spine. You are free to think that it is not a Dream Theater song, it's just that if you think that, you are objectively wrong.