Are you sure?
Yes. As I read it, the author is concerned about his work, not some Debian trademark.
I think the swirl is such a protected thing, that will be handled by debian like the color magenta of "Deutsche Telekom".
You are wrong. The only protected element in whole Debian is its name. That's why nobody can put it on a whatever GPL-ed wallpaper.
But the swirl is GPL-ed and as such alterable by everyone.
GPL and Trademark do exclude each other.