Highly likely that the source came from inside the GTAA. Most likely the source did not want to be named because it seems GT was not wanting the info released. Unnamed sources are a staple of journalism. It's on the reporter to verify info prior to printing. If KS is wrong he opens himself and the AJC up to legal issues. Gotta think his editor is on top of this as well.
I don't doubt that the source was from inside the GTAA. If GT didn't want the information to be released, the I personally wouldn't label the person as a "spokesman". Also, if the GTAA didn't want the information released it is likely that not everyone in the GTAA had absolute knowledge of everything.
I don't believe there are any legal issues even if the report was wrong. It isn't libelous. It isn't defamatory. And it is about a public figure. I don't see any way that there is any legal issue at all, but I am not a lawyer.
If you pay attention to the AJC and their sports reporting, they will have similar reports post at the same time about the Falcons, Yellow Jackets, and mutts. "Five Reasons for ...." or something like that. Their mutt section reports all kinds of things as "breaking news" type stories, or which many are speculative or just flat out wrong. I believe that KS is under pressure to "get" stories. He has a history of reaching around official channels when he can't get the information he is asking about. I highly suspect(but don't know) that he asked people at the GTAA until somebody said something. I have little confidence in his stories about things like this, especially since he was the only one that I saw reporting it. I appreciate what KS does, but I have to temper my understanding of his stories with what I think he does well, and what he doesn't.