Facebook messenger "active now/ active xm ago"

Well, it all started with curiosity. 

When you use the facebook messenger app, you will something on top indicating whether the person is "active now" or "active xm ago". 

So to satisfy my curiousity, I conducted a short experiment and I have found out that; 

- If you go on facebook, a person on messenger will see you as "active now". 

- If you open your messenger app but do not open any messages, a person on messenger will see you as "active xm ago". Meaning the last time you open a message or go on facebook. 

- However, if you open your messenger and you proceed to open a message (doesn't matter if you answer or just viewing the message), your time status will be "active now". 

Just as a reminder, this so called experiment of mine was for my phone so I don't know if it will be the same for a pc/ laptop. :) 

I didn't find any satisfying answer elsewhere so I decided to check myself. 

Hope you guys got something from this post xx