Huh, surprising to me that I'm listed as an owner of the arc organization on notabug.org! Did I click on something without realizing what I was doing? I don't see any email from notabug.org about the new organization in my email or trash..
Do you happen to remember how long ago this was? If it was more than 30 days ago I may well have accepted and forgotten, and see no trace of it in my email's trash.
Adding people to organizations without informing them seems like a bad idea. It's also not what GitHub does, and GitHub is who all these sites are copying, so shouldn't be happening.