blase I think if it were truly angry it'd be acting more aggressive... maybe they just don't have much of a vocal repertoire.
baleen Kangaroos, unlike wallabies, have strong tails which they can lean on. Kangaroos can't sit down, but instead lean back on their tails. One sign of aggression is when they stand upright and lean far back on the tail, which means they are rearing to kick an opponent with their legs.
These guys look pretty small, but still if the guy had been kicked it would have been extremely painful. Not unlike getting an actual punch to the face.