He's referring to the XDG standard [0], I think. It used to be that all persistent user-configuration resided in ~/.${appname}, but some people were unhappy with that so they recreated the etc|var|lib|tmp filesystem usage distinction inside users' home directories. This means that an application's user files are now spread across $XDG_DATA_HOME, $XDG_CONFIG_HOME, $XDG_CACHE_HOME and $XDG_RUNTIME_DIR.

[0] https://specifications.freedesktop.org/basedir-spec/basedir-...