In this case yes, but on the other hand Red Hat won't publish the RHEL code unless you have the binaries. The GPLv2 license requires you to provide the source code only if you provide the compiled binaries. In theory Meta can apply its own proprietary patches on Linux and don't publish the source code if it runs that patched Linux on its servers only.

I'm more surprised that the scheduler made for a handheld gaming console is also demonstrably good for Facebook's servers.

Exactly. Once the work is upstream and open, it stops being "Valve's thing" and just becomes part of the commons

I mean.. many SteamOS flavors (and Linux distros in general have) have switched to Meta's Kyber IO scheduler to fix microstutter issues.. the knife cuts both ways :)

Well if you think about it, in this case the license is the 30% cut on every game you purchase on steam.