Are you sure about that (whatsapp)? I mean how does one get messages just after exiting the app (the back button exit) if the service is updated only once in 30 minutes? I am asking just because I am curious, and since you are developing for WP, I guess you'll be in a better position as compared to me to answer this
Yes. What i said is right. It is the push notification we get when the app is not in foreground.