Yikes. I wasn't planning on working at GitHub, but I definitely wouldn't if that quote is genuine.
Imagine actually being forced to use VS Code to do your work. I love VS Code, but it seems wrong to center the team's workflow around it. I guess you're screwed if you want to use Vim or Sublime?
"Oh, but there's plugins for that!", I can hear someone say.
Yeah, f--- that sh--.
And after all, who's to say that GitHub Codespaces won't someday drop VS Code when it's no longer in vogue? GitHub Classroom touted its Repl.it integration and then deprecated it almost immediately without an equivalent alternative (just use VS Code bruh), so it's not that farfetched.