Settlement crack - is this one?
Well, one thing that doesn't make any sense based on the picture is this part:


  Basically the area of wall is made up of two sheets of plaster board and at the join the plaster board has been broken through 


I'm not even sure it looks like this, but in any event, how exactly would you have cracked this without causing any other damage to the wall?  Like if you had banged the wall so hard as to crack a seam, you'd expect to see other damage to the wall.  

Assuming these cracks do line up to the seam, two things come to mind. (1) The boards were not staggered properly and (2) The installer likely did not use paper or fiberglass tape on the seams - I think it looks more like a crummy installation.

At the end of the day though, this isn't really a serious issue, more of just wear and tear; all walls get banged up to some degree. The owner should just sand, patch and paint it and move on.