I noticed that blog post only mentions "WSL" not "WSL 1" or "WSL 2". It appears this post is just talking about WSL 2. This seems to be the trend coming from MS: "WSL" is referring to WSL 2 only. I guess WSL 1 is becoming deprecated.
Noway if I need systemd, I can try to run in on WSL1 and this won't change.