It is hard to say but my initial guess is that since I see what looks like a shower curtain rod right below this damaged area, that I would think it might be plaster damage from a previous shower curtain rod mounting.
When talking about shower curtain rods there are really two types, compression and mounted. Mounted rods are superior in strength and cause less damage to the wall, but take a bit longer to install.
Compression rods apply horizontal force to hold the rod against the wall. They are not as strong and can fall rather easily. They can also pretty easily be installed too tight to where it cracks or damages the surrounding plaster or drywall. If it is mounted properly and sombody were to pull down on it before relieving the tension then that is another way that these types of rods can damage your wall.
I have seen similar damage around the edges of shower surrounds before caused by compression shower curtain rods.
That makes sense now that I look at it that it is a shower head pipe, there isn't enough room on the side to justify a shower curtain rod.
Apparently there must have been a shower head above that new shower head at some point in time. What you are seeing is either an incredibly amateur or incredibly lazy attempt at repairing the hole in the plaster wall where the previous shower head existed.