Maybe its somebody's sick act or maybe the dog is really really hungry or thirsty and found this container containing some food/water in it. So it stuck his head in and couldnt pull it out.
Whichever way, lets hope someone gets the head out of the container as soon as possible. If its really an act of man, that fella shall go to hell and have their heads forced into an unbreakable gold fish bowl for eternity.