Hadn't even heard of the rug incident until I read about it in this thread, but I'm pretty sure their idea of meritocracy here only applied to GitHub the company, not GitHub the website, and came out of their culture of "Managers and chain-of-command? Not here. You can work on whatever you want at any time and at any location, as long as good work comes out of it."
If you "succeed" and do "well" on GitHub (what metric can we use? Lots of a stars? Getting your name out there?), what does that actually prove?
If GitHub is a meritocracy, what have the "winners" done to set them apart from the rest, and how does that translate into the professional world?