I'm not even sure the poster you're responding to is correct on a technical level.
My understanding (possibly flawed) is that github started by using the current git tooling but that they soon started running into issues because the CLI tools were never meant to scale and never as a web application.
So they wrote their own implementation of git (their own tool that understands git repositories) but did so in a way that's more compatible with the scale and the web-oriented work they do.
So it's not even clear to me how much of the actual code they have running is open source.
They make money off the code hosted on Github, which is by-and-large open source. Github makes money off of open source software whether they themselves run open source software (almost certainly yes) or not.
The question posed is how does github make money off of OSS in a way that other similar services do not. Since they all host OSS software in one form or another, that observation isn't relevant.
My understanding (possibly flawed) is that github started by using the current git tooling but that they soon started running into issues because the CLI tools were never meant to scale and never as a web application.
So they wrote their own implementation of git (their own tool that understands git repositories) but did so in a way that's more compatible with the scale and the web-oriented work they do.
So it's not even clear to me how much of the actual code they have running is open source.