Being I work at a Seaport Terminal, I can totally see this happening:

The "Forklift" type machine is called a "Top-pick" it's sole use is to pick up Containers you see on ships and load them on chassis trailers for truckers.
It's pretty obvious (to me) what happened here, the operator went a tad too high with a load and the top-pick got too top heavy. It does happen albeit rarely. The operator was probably a newbie Longshore worker!