The tone. I assume that if the author does not want people to distribute the library in an application with DRM, regardless of the fact whether they publish the source code or not they would also not be happy if somebody just took it, modified it and sold it as service without publishing their code.

Let's maybe generously assume that the author is not dumb and would carefully choose a license based on his needs and preferences.

Then consider the facts: The work is based on GPLv2 licensed tool (gifsicle), thus subject to the same terms and conditions. Knowing that, one can read the note as a friendly reminder of how the ToS of the Apple store is incompatible with GPLv2. You may have read it as snark, but it's literally just stating a matter of fact regarding a matter the author of the fork can't legally do anything about.