Besides that, in this timeline Glenn is still very much alive for quite a long time. Rick's group is still sitting outside Atlanta at this point in the Walking Dead game. We aren't even to winter yet, and they don't leave there until winter is under way. Rick still hasn't been to Wiltshire, Hershel's farm, the prison, etc. They haven't been anywhere, or really started there journey at all yet.
Besides, all we know about Negan is that he has set up near D.C. We have no evidence or any reason whatsoever to believe he came from down south in Georgia. Actually, that would be incredibly stupid story wise to think that he just happened to come from the same places Rick came from. He could have come from literally anywhere, or has always lived near D.C.