Bull rush is a Move. A Move you share with a victim that also specifies the victim draws AoOs as well.
i strongly recommend not extending this to Falling, Telekinesis's Violent Thrust option, moving platforms of any nature or any other change of position that does not specify AoOs are drawn.
A bull rush is special attack action and not a move action.
BULL RUSH
You can make a bull rush as a standard action (an attack) or as part of a charge (see Charge, below).
Now if you succeed in the bull rush attempt you may elect to move with your opponent but the bull rush is not a move action since it is specifically a standard action (attack). I would say it was essentially amove actin following the standard action but that is not true since you can do a bull rush as part of a charge and still move with your opponent as part of the bull rush if successful (and normal movement limit is not exceeded).
Bull Rush Results: If you beat the defender’s Strength check result, you push him back 5 feet. If you wish to move with the defender, you can push him back an additional 5 feet for each 5 points by which your check result is greater than the defender’s check result. You can’t, however, exceed your normal movement limit. (Note: The defender provokes attacks of opportunity if he is moved. So do you, if you move with him. The two of you do not provoke attacks of opportunity from each other, however.)