In a closed source situation people using a pseudonym don't just randomly approach a company and say "hey can I help out with that?"

It was caught by sheer luck and chance, at the last minute - the project explicitly didn't have a bunch of eyeballs looking at it and providing a crowd-sourced verification of what it does.

I am all for open source - everything I produce through my company to make client work easier is open, and I've contributed to dozens of third party packages.

But let's not pretend that it's a magical wand which fixes all issues related to software development - open source means anyone could audit the code. Not that anyone necessarily does.