The claims are well into the "I found a unicorn" territory, I'm tipping its either "If you misconfigure this, its unsafe", or its a real vuln, and its significantly harder to exploit that they are claiming.
That’s not all GNU/Linux though. Either the OP doesn’t understand a very common container OS, Alpine, doesn’t use systemd (also Void Linux and others outside the container space) or it’s something else.
If this is true (or at least plausible to the relevant people), the author of that Twitter post will probably be on the radar of any shady government agency worldwide. Not a nice situation to be in.