System programming languages also used to refer to non-scripting languages. See this paper by John Ousterhout (creator of Tcl) written in 1997: https://users.ece.utexas.edu/~adnan/top/ousterhout-scripting...

I don't think so. I think it's just the way Rob et al. used the term from their previous experience.

It's not meant to mean operating systems language, nor embedded systems language.

Rather for writing parts of a systems, such as servers. I would say that the definition is not that far away for Java or C#, but the expectation is simply that it would be "lower level" components of a system, including unix like utilities.