I have been assaulted and defended myself multiple times in Canada. It's not how you're describing it where you have some duty of care for the person you're actively defending yourself from. Your right to defend yourself logically does not include the right to counter-assault or murder others. Guarantee this guy could have stopped but didn't. That's 99% of the time what constitutes unreasonable force.
Plenty of people hospitalize their assailants and don't get charged. This story is rage-bait.