You're right, it'd have been very appropriate, but I back when I recreated those graphics and added it into the game, I forgot to make an entry in the credits database. I hate to admit that in pretty much every game I've made, I've accidentally forgot to add at least someone to the credits.
Since we're on the topic, Simon was one of my closest friends. He had this amazing (and sort of weird) sense of humor. He managed to simultaneously be quite sarcastic and occasionally offensive and inappropriate, at the same time being one of the most loving and caring persons I've known. His strong personality has affected my own to the degree that I wouldn't think or do the same things as if I had not met him. I've drawn quite a bit of inspiration from him in Knytt Underground, and he also created content for my previous games. Usually he'd come up with the weirder things, like Das Magdenburska Martian Deathray Panzer Crawler in Knytt, and the idea for the guy walking past the screen in the end of Within a Deep Forest with a lantern in his beard (and the voice you hear is him). Of course, also the Ortofaktor tileset in Knytt Stories.
As you probably guessed since I'm talking about him in the past sense, he died. It was a little less than a year ago. Strangely, I never had a problem accepting what happened. Maybe because I know losing a close friend is an experience I share with a lot of people, most likely including several of you who read this post. I miss him a lot though.