When hitting a zombie pigman, the ones within a reasonable area will become angry and the ones further away will not. You can read more on the way they behave in PC here http://minecraft.gamepedia.com/Zombie_pigmen.

Steps to Reproduce

• In the nether, go to kill a zombie pigman (your sword must not be able to kill
  them in one hit)
• Notice the pigmen around the one you hit. Only a few will be angered, and more will not get angry