It's hard to believe in 2022, Google, Amazon, FB etc .. all use Linux, all CDN use Linux as well, and some services serve even more traffic than Netflix ( Youtube ). BSD faster than Linux is a myth, the fact that 99% of those run on Linux means more people worked on those problems means it's most likely always faster.
The funny thing is the rest of Netflix runs on Ubuntu, only those edge CDN runs on BSD.
Disclaimer: SRE at Google on a team vaguely related to video CDN stuff, but have no inside knowledge
I don’t think you can dismiss BSD faster than Linux (or make any claims about the relative speed of different OSes) just because big companies run Linux. There are other costs involved and optimisations that can be shared if your edge serving stack is as similar as possible to the non-edge serving stack (that you have many more engineers developing for).
All you can conclude is that with enough optimisation, Linux can be made to perform well enough for it to not be worth replacing (yet). Because replacing Linux would require replicating all the custom software and optimisations made to it for whatever other platform you pick.
It worked faster. It's a common misconception among newbies that "Linux has NUMA" automatically means it will use NUMA properly in a given workload. What it actually means is you _should_ be able to use existing functionality. Sometimes you'll only need to configure it, sometimes you'll need to reimplement it from the scratch, and doing that in FreeBSD is easier because there's less bloat.
The funny thing is the rest of Netflix runs on Ubuntu, only those edge CDN runs on BSD.