I doubt it's related. DZ left GitLab a while back, and even then his involvement had been limited for quite some time. Knowing GitLab and its history of security vulnerabilities, the timing is probably just a coincidence.

There has also never been any evidence of e.g. state actors sneaking in backdoors and what not. The code review process is quite extensive (probably a bit too much even), so it would be difficult to sneak in vulnerabilities deliberately. It's much more likely these issues are caused by growing complexity and the amount of functionality that GitLab supports.