> As for the Systems Programming section, does he really think that knowing how a compiler works is a system-related topic?? and why is that level 1? shouldn't the first level be understanding things like system calls, filesystems, drivers, kernel operation?

I think the idea is that most people will start exploring the world of programming from higher layers working their way down. People use software, then they write software with tools (languages), then they try to understand the tools, then they try to understand what the output of the tools mean on a yet deeper level, going down the rabbit hole all the way down (to physics? but I guess the lines is drawn elsewhere).

This may be wrong but it's obvious from the rest of the matrix that this is probably just based on how the author and maybe their friends gained "proficiency".

None of this is generally applicable. I do think the,matrix is still valuable. It provides a view of how some people may evaluate competence (even if misguided wrt ordering/levelling) and provides a set of goals that are not bad per se. Being on the highest levels mentioned there does probably in fact translate to a certain high degree of experience and competence.