That guy deserves a punch in the head for not controlling his dogs and letting them go after roos to begin with.Wow...was that totally necessary? He let go of the dog what would the roo have done if the man just calmy backed away at that point?
The kangaroo was a male and it was defending itself from the dogs and considered the human as a threat and an intruder into his territory. Dingoes are a breed of dog that actively hunt kangaroos so the roos are careful around any dog.
Male kangaroos also have territories and defend them from other males. Male roos don't hit, they use their arms to grab and hold the opponent, then kick hell out them with their back legs. They lean back on their tail when doing this, and they have sharp claws and can rip open a human with a single kick. Male roos have thicker skin around their abdomen area specifically for this purpose (so they don't get torn open by an opponents kick).
If the guy backed away the roo might have gone after him or might have let him go. It depends on the roo. Some will go after intruders and chase them out of the area. Others will just let you back away. But the guy should have had better control over his dogs and not gotten into that situation to begin with.