I used to have pet kangaroos, but even they would still rear up when startled because they feel threatened. Wild kangaroos are only dangerous when cornered and they feel the only way they can escape is to go on the attack. Their first instinct is to bounce away if they hear you coming (they have excellent hearing).

My guess is this guy accidentally surprised a kangaroo that was sleeping in bushland and the kangaroo felt it was cornered. When his workmates suggested he punch it back in retaliation, that would have been the worst thing he could have done. The kangaroo would have probably reared back on its tail and given him a powerful kick with its extremely muscular legs. He could have broken bones or there's even cases of dogs being picked up and disembowelled by angry panicky kangaroos that are being barked at.