From my limited experience, lighttpd has non-stellar documentation and the community (including devs) is kinda rude. nginx has better documentation and a much more welcoming support community. At least for the tasks I use it for (proxying a bunch of random services on a home server), the syntax is a lot easier than lighttpd and it's easier to bring in goodies as modules that would require recompilation on the lighttpd side. It might be a bit of a chicken-and-egg problem, but the nginx binaries are also a lot of up to date in the package managers I used. On a raspberry pi I ended up needing to compile from source to get a modern version, which got kinda annoying.
Not sure which year (decade? :P) you're talking about but in the beginning (before 2010, maybe 2007-08?) Jan was still kinda involved in the German PHP scene and I can't imagine that to be true, I only remember good interactions and we were one of the heaviest users of lighttpd back then. But the docs were never that great, and it seemed to be a one man show, later with a very small team, that's when I think it stalled and only picked up pace years later.
But there indeed came a time (maybe 2010ish?) where nginx took the lead with gread strides and most people (even the die-hard fans) mostly moved to nginx, that's about when it was clear that it would probably win and stay for the forseeable future. Back in those circles at least (see some other comments for the PHP FPM story) Apache was only kept for setups with lots of different other dependencies, like mod_svn or webdav, if you "only" needed a webserver to front PHP it was nginx.
I also remember many people holding out on adopting Apache 2.2 for a looong time.
