I'm not saying it is, I'm saying this is what it feels like for him and that I can understand the feeling.
Also, flatpak doesn't only compete with "AppImage or just running random binaries you find or compiling it yourself". It competes with the package manager, that has worked well for decades. The package manager has issues as well.
Maybe from the authors perspective it looks like everyone wants to throw away the package managers because of some issue they have, instead of tackling these issues. If he then points out the flaws in flatpak, people say "sure it has some issue we need to fix".