Obviously, I wasn't mentioned. I never interacted with that project. I haven't heard of it before.

This is a constant annoyance. GitHub spams notification mails for spurious reasons ("your two-letter user name occured inside a large binary blob" – yes, really!), for bad reasons ("someone tried to make his repo known and mentioned you"), and for no reasons (like this today).

GitHub's support doesn't care. More eyeballs for repos are good for them.

There are so easy mitigations: don't notify people unless they have already interacted with a repo. Don't notify people if their username isn't mentioned with a "@" in front of it and a " " after it.

And I'm pretty sure I switched off all notifications in GitHub's settings the last time I was annoyed by it. Just went there, all notifications are switched back on.