Here's some info on sending offs and my explanation of the call:
First of all direct free kick offenses are not at all related to a yellow card or a red card when committed in the penalty area. They become penalty kicks when committed within the 18 yard box. The addition of a yellow or red card is a secondary action and is not mandatory.
Direct Free Kick
A direct free kick is awarded to the opposing team if a player commits any
of the following seven offences in a manner considered by the referee to be
careless, reckless or using excessive force:
• kicks or attempts to kick an opponent
• trips or attempts to trip an opponent
• jumps at an opponent
• charges an opponent
• strikes or attempts to strike an opponent
• pushes an opponent
• tackles an opponent
A direct free kick is also awarded to the opposing team if a player commits any
of the following three offences:
• holds an opponent
• spits at an opponent
• handles the ball deliberately (except for the goalkeeper within his own
penalty area)
A direct free kick is taken from the place where the offence occurred
(see Law 13 – Position of Free Kick).
Penalty Kick
A penalty kick is awarded if any of the above ten offences is committed by
a player inside his own penalty area, irrespective of the position of the ball,
provided it is in play.
Sending-off Offences
A player, substitute or substituted player is sent off if he commits any of the
following seven offences:
• serious foul play
• violent conduct
• spitting at an opponent or any other person
• denying the opposing team a goal or an obvious goal-scoring opportunity
by deliberately handling the ball (this does not apply to a goalkeeper within
his own penalty area)
• denying an obvious goal-scoring opportunity to an opponent moving
towards the player’s goal by an offence punishable by a free kick or a
penalty kick
• using offensive, insulting or abusive language and/or gestures
• receiving a second caution in the same match
We have to assume that Kewell this rule is the reason for the red card. However, considering the lack of extension of Kewell's arm and the placement of the ball on his body at the time of deflection (upper arm and chest) it can be assumed that there was not intent to illegally deny a goal scoring opportunity. Still, the referee followed the rule to a T and the call is fair because Kewell's play denied a goal scoring opportunity, not because a handball in the box is considered to be intentional.
If the handball was away from the goal line the call would have been a yellow plus the penalty.