The aim was definitely to make it a fun piece, at the time. I remember selecting some kind of polysynth instrument on my keyboard, and just thinking about the band's style, and I started creating it. I made the entire peice in one go, from start to finish, without thinking too much about the progression I wouldn't really say that much improvisation was involved, since I had a surprpsingly clear idea of what I wanted to do. Every now and then I guess composers get lucky, ~inspired~ this way. I occasionally make songs where I simply start composing at some point, and then just roll with it; I even wrote a blog post about this style of composing long ago (not going to link it because it's old and bad, haha).
There are so many different ways to compose, and to think about composing. Right now, I'm working on a piece where the ending was finished long before the middle sections. In fact, there are still a few parts to clean up. It'll be my best solo piano piece of the year, for certain (I hope I manage to finish it this year; I am almost finished. I just need to be able to play it well too, which is turning out to be more difficult with my newer and more advanced compositions).
So long side-notes aside, the reason this reminds you of an improvisation, is probably because I created it in order from start to finish, and simply quit when I decided I was done. I don't remember on what timescale I did it anymore, but I'm guessing it probably only took an hour or so.
That said, I think the piece stays true to the theme throughout, and there is even some hidden repetition in there. I think I could've easily made this into a full-length (whatever that even means in regards to music, but I mean a 3-4 minutes long) piece, only repeating the chord patterns and melodies that are already in there. But alas, I did not. Well, I guess I don't necessarily regret it.
I did have to relearn the piece! Surprisingly, I remembered most of it since I find the melody to be pretty catchy, and most of the chord choices simply make sense with that in mind (adding to that, the arrangement doesn't really change around all too much). But I think I spent some 10-15 minutes refreshing my memory using the old MIDI file, before I was able to play this piece from start to finish again.