I know nothing about how flatpak works other than that it's containerized. But this meme tells me it's the OS's responsibility to create the flatpak, and not the developer's? Is that right?
No the most common way is for devs to package their own software as a flatpak since you can typically choose your preferred packaging tool to use inside of the flatpak.
Traditional package management typically is done by the distro maintainers.