Because some Blitzers have appeared to have gone full Essington mode, these are definitions and interpretations from the most recent public and readily available PDF of the AFL's rules (2013)
Kick or kicking: in relation to disposing of the football, means making contact with the football with any part of the Player’s leg below the knee.
Mark: has the meaning described in Law 14.1.
14.1 Definition: A Mark is taken if, in the opinion of the field Umpire, a Player catches or takes control of the football: (a) within the Playing Surface; and (b) after it has been Kicked by another Player a distance of at least 15 metres; and (c) which has not touched the ground or been touched by another Player during the period when the football was Kicked until it was caught or controlled by the Player.
--> note, to constitute a mark it needs to meet ALL requirements as implied by the "and" between (b) and (c)
12.1.1 scoring a Goal Subject to Law 12.2, a Goal is scored when the football is Kicked completely over the Goal Line by a Player of the attacking Team without being touched by any other Player, even if the football first touches the ground.
15.6.1 when awarded A Free Kick shall be awarded against a Player who: (a) Kicks the football Out of Bounds on the Full;
So, reading all that it is quite clear that a "kick" constitutes any contact, whether intentional or otherwise, between the ball and a player below their knees.
We also know that for a mark to (correctly) be paid, the ball must be kicked by another player.
Given that the ball made contact with Ambrose's foot which constitutes, by the AFL's own definition, as a kick he should not have been paid a mark.
If anyone disagrees you're more than welcome to read through the 96 pages to find something that overrides a) the definition of a kick and b) law 14.1 regarding what constitutes a mark