Because he tried to update a system-wide flatpak install as a non-root user. Flatpak uses polkit for root permissions. Polkit is usually set up to allow non-root local users to update flatpak without a password, but not remote ones, hence having to continually enter the password for polit when using SSH. He could just run the update with sudo like a normal package manager and would only have to enter the password once. But then he wouldn't be able to complain on Lemmy.