To the extent copyright applies to such information (which would vary by jurisdiction and the details of the information), it most certainly doesn't fall in the "public domain" (a widely misused term). You've granted Github a license to use it, and Github allows others to view it. The question then becomes whether users of Github's API may copy that information. Legally, Github has the ability to grant permission to third parties, so if they choose to do so, you can't un-grant that permission, because you've already granted it to Github. However, Github doesn't have to grant that permission, and may set conditions on it via their ToS and their API ToS. And it doesn't seem entirely clear whether Github's ToS allows what Gitpay has done.
Legal issues aside, though, scraping another service to create pseudo-accounts and refusing to provide even an opt-out does not seem like a good business practice. While Gitpay appears to have done several things right that other services get wrong, this definitely isn't one of them, and it needs fixing.
Legal issues aside, though, scraping another service to create pseudo-accounts and refusing to provide even an opt-out does not seem like a good business practice. While Gitpay appears to have done several things right that other services get wrong, this definitely isn't one of them, and it needs fixing.