Not sure, I know iron golems used to attack pigmen and it didn't trigger pigmen to attack the player. And I think it didn't start until much after the bug you mention started.
Iron golems are unique in that they are naturally hostile to pigmen, where as the bug you state requires the player to intervene and get a skeleton or something to attack a pigman, and then for the player to kill the skeleton. It could be the case that all that is required for the bug is that the pigmen become hostile to a mob and that mob to die (so lets say they manage to kill the iron golem or skeleton without the player killing either) and then, still being hostile but their hostile target being dead, so they remain hostile and default to the player.
So I'm not sure. I think they're unique bugs, but they could be involved somehow.
Joke Shot
Not sure, I know iron golems used to attack pigmen and it didn't trigger pigmen to attack the player. And I think it didn't start until much after the bug you mention started.
Iron golems are unique in that they are naturally hostile to pigmen, where as the bug you state requires the player to intervene and get a skeleton or something to attack a pigman, and then for the player to kill the skeleton. It could be the case that all that is required for the bug is that the pigmen become hostile to a mob and that mob to die (so lets say they manage to kill the iron golem or skeleton without the player killing either) and then, still being hostile but their hostile target being dead, so they remain hostile and default to the player.
So I'm not sure. I think they're unique bugs, but they could be involved somehow.