This does not surprise me all that much. Note that if you merely intend to punch someone and they fall in a bad way and then die, it would also not be called an 'accident' even if there was no intent to kill, only intent to harm.
(just in case it's not clear I'm agreeing with you here)
So I had a case years ago. It's this guys birthday, he goes out to the bar. After the bar closes he invites a bunch of people over to his house. One of the people he invites over takes a decorative sword off of the wall and is playing with it. The homeowner takes the sword from him, pokes the guy with the point of the sword in the chest and tells him to leave his stuff alone.
Nobody thinks anything of it at the moment until the guy collapses 10 minutes later. The sword was really sharp, went into his chest, nicked his heart. He was rushed to hospital, almost died.
In this case the Accused could have been guilty for the offence of "aggravated assault". If the guy had died he 100% would be guilty of manslaughter. He intended to use force against the guy without his consent, and is responsible for the consequences, even though there was 100% no question he didn't intend to actually hurt the guy.