With sufficient data points, you can do A/B and see that all affected systems run a specific version of Linux distro, and eventually track it down to a particular package.
Even then, who actually has a massive fleet of publicly exposed servers all running a mix of distros/versions? You might run a small handful of distros, but I suspect anyone running a fleet large enough to actually collect a substantial amount of data probably also has tools to upgrade the whole fleet (or at least large swaths) in one go. Certainly there are companies where updates are the wild west, but the odds that they're all accessible to and controllable by a single motivated individual who can detect the exploit is essentially zero.