None of this explains why @Life_Happens got a PM while visiting a model in invisible mode that he hadn't visited beforeIt was possibly just an educated guess. If you usually go on and see them at a specific kind of time, they may have randomly PMed you, then you read the message and it "confirmed" the guess.
Or of course, there could be a bug and the green dot shows to the model to show you're online. I think it's the former though