This was on the "unstable" branch of Nixos, the branch that became the stable branch today, which is the occasion of this story on HN we are commenting on.
Digression: the reason I chose the unstable branch instead of the then-stable branch (named Nixos-20.09) was that I wanted to achieve an "all-Wayland" environment as quickly as practical (and in fact all of the apps running on my machine right now and for the past few weeks talk directly to Wayland without the interposition of Xwayland). And the reason I wanted to jump ahead to an all-Wayland system is that although I knew Linux pretty well, I knew very little about X11, and I reasoned that since X11 is slowly going away anyways, I would prefer to avoid spending any time learning about it and would prefer to avoid having to get used to its quirks. (End of digression.)
You cannot just install Chrome from Google's web site on Nixos: unless someone has compiled it for you, you have to compile it from source and more distressingly you have to configure the compilation extensively to have any hope of the resulting binary actually running. For example, glibc on Nixos is not in a standard location, but rather all of the files in the glibc package are under a directory with a name like /nix/store/8f9f6724fd2341d9f2bc758cf9e43830d23d37a3-glibc. Well, of course the code that compiles Chrome needs to be informed of that location and of the locations of all of the other packages it relies on, e.g., the system's libraries for drawing GUIs on the screen. This job of configuring the compilation is mostly easily done by writing something similar to a declarative build script in the Nix language, so of course that means I would've had to learn a new programming language in order to patch the zero-day exploit in Chrome before the maintainer of the google-chrome package got around to it (which I never did).
Sadly, I did not have time back then in early March to install the stable version of Nixos to determine whether these zero-day exploits had remained unpatched there, too. (I did verify that the package "chromium" was at the same vulnerable version as the package "google-chrome" was.) So I guess the purpose of this comment is that there are preliminary signs (namely, the fact that nowhere was I warned that the unstable branch might have gaping security holes) that Nixos does not get as much attention from security-knowledgeable maintainers as some of the other Linux distros do -- or at least that the security attention it gets is concentrated on server use cases with desktop use cases being relatively neglected.