"Manslaughter - The unlawful killing of one human by another without express or implied intent to do injury."
What the police officer did was manslaughter, end of.
It is just pure bad luck the guy died yep, but it was determined the police officers actions attributed to his death, thus the prosecution is justified.
If you or I had done the same thing we would be prosecuted too, being a police officer is no different.
And yea, luck is the only deciding factor, he could have fallen and suffered nothing more than a bruise, but he didn't.
So its not a ridiculous world for this reason, though maybe for many others!