http://seclists.org/oss-sec/2016/q3/231
(and it was not even my project... I just reported the bug)
Now the workflow changed a bit, in the link that you shared in fact it says "For open source software products not listed below, request a CVE ID through the Distributed Weakness Filing Project CNA." which is just an easy-to-fill Google form. Not such a close system as you seem to imply
(OTOH, obviously CVE cannot guarantee or pretend to have universal coverage of every security issue ever existed)
I generally like systemd, but it's irresponsible to not publicly communicate about such an issue if you're aware that it's actually a security issue
fix bugs before investigating, that's ok... but not communicating it means that you'll leave users downstream exposed to it, since it won't prompt maintainers to ship the patch/upgrade