None of the tools the author mentions as following XDG, actually follow XDG. No default tools shipped with macOS place files under .config or anything like that. There is a bunch of dotfile vomit in $HOME and that's it. Every tool that uses .config is one you manually install from an external source.

The XDG spec is to coordinate the userspace of Linux software, meaning both CLI apps and windowed apps. Linux needs things called standards because Linus has not bothered to write them down himself, so there is no equivalent of Microsoft telling you data goes in AppData and Apple telling you data goes in Library. Identifying it as a standard for CLI tools across OSes is just wrong.

When CLI tools do this on macOS, it is not because anyone thought 'this is a standard for macOS', it is because they thought 'with -target darwin I don't get any compilation errors. ship it!' and frequently use those locations on Windows too where they don't make any kind of sense at all.

The standardized location is Library. If you do not expect it, that is on you; you should expect it, as it is the standardized location. It is only just now that people are starting to catch up with it, instead of blind ports with absolute minimum macOS-specific code, because of libraries like `dirs` which make it easy.