[fauigerzigerk]

Wikipedia says:

The primary distinguishing characteristic of systems programming when compared to application programming is that application programming aims to produce software which provides services to the user directly (e.g. word processor), whereas systems programming aims to produce software and software platforms which provide services to other software, are performance constrained, or both https://en.wikipedia.org/wiki/System_programming

By that definition it seems pretty clear that systems programming covers a lot more than just operating systems. But calling a language a systems programming language if it is unsuitable for writing operating systems seems a bit unusual. At least it would have been unusual at the time these terms were originally coined.