Where Are They Hiding?

Stumbled upon this site by pure accident, but during some investigative research and since I have yet to find the answer, I felt this might be a great place to ask my question. Setting: I have an iPhone and an iPad mini both running on iOS 7. I have a laptop as well that I am currently logged into Facebook on, my chat is off and I have not commented or liked anything. There is nothing new posted on my timeline. My iPhone and iPad have the Facebook app on them, I am browsing through Facebook when I get a message on my iPhone through the new Messenger app of a message just sent to me, so I get on my iPhone and access the Messenger app to read the message and it states from a friend, "I see your up." So of course I respond by asking "and how did you know that?" he replies "because I see all." I reply, "Damn, I was hiding. Guess it wasn't a very good spot." He says, I have a very special iPad that lets me see everything." because of a bet, he leaves me with that and I am just hanging here. But I am dying for the answer......I have heard stories about the new facebook messenger app and find it interesting to say the least. Question: How in the hell could he "see" me? I didn't think I left any traces and thought my "hiding spot" was covered well enough. Please tell me.....