Tbf 500ms latency on - IIRC - a loopback network connection in a test environment is a lot. It's not hugely surprising that a curious engineer dug into that.
It started with ssh using unreasonably much cpu which interfered with benchmarks. Then profiling showed that cpu time being spent in lzma, without being attributable to anything. And he remembered earlier valgrind issues. These valgrind issues only came up because he set some build flag he doesn't even remember anymore why it is set. On top he ran all of this on debian unstable to catch (unrelated) issues early. Any of these factors missing, he wouldn't have caught it. All of this is so nuts.
I've seen that claim a couple of places and would like a source. It very well may be since Microsoft prefers Debian based systems for WSL and for azure, but its not something I would have assumed by default