As others mentioned "systems language" isn't well defined. If you want to define a "systems program" as one with hard real-time requirements, then no, Go isn't a very good choice; however, the article defines it differently (such that `wc` satisfies), and demonstrates that Go satisfies that definition.

That said, it's better to use terms that map better to a set of requirements, such as "hard-realtime" or "soft-realtime".