Sice the need for intent was removed from all penal offences except handball within Law 12 the very fact that the player, albeit inadvertantly; kicked Joe made it an offence. It being in the penalty area made it a Penalty.
The challenge however obviously was not considered to be 'reckless' in the opinion of the Referee and as this is a necessity when cautioning for challenges no caution was issued.
With regard to the perceived lack of a caution for kicking the ball away a caution is only appropriate if the action of kicking the ball away is a) an act of dissent or b) an attempt to delay the restart of the game. Unfortunately Asa kicking the ball away delayed the taking of a free kick and hence by definition the restart of the game.
I hope that this helps clear up any confusion over this issue