alt Hacker NewsFun story! Performance is often highly unintuitive, and even counterintuitive (e.g. going from C++ to Python). Very much an art as well as a science.
Crazy how many stories like this I’ve heard of how doing performance work helped people uncover bugs and/or hidden assumptions about their systems.
It doesn't come off as unintuitive by my read. They had a bug that led to a massive performance regression. Rewriting the code didn't have that bug so it led to a performance improvement.
They found that they had fewer bugs in Python so they continued with it.