No, they're saying that systemd provides many of the same benefits that running things in Docker provides.

No, he's saying that isolation via systemd is basically the same kind of isolation that you get with runtimes like docker. It's just Linux namespaces, which conventional wisdom is to assume that it's a relatively modest security boundary at best. The key takeaway here is that you can get this added security with minimal to no performance impact in a way that's simple and straightforward for the sysadmin to configure.