A topic from AEG's L5R CCG Rules forum, copied for Oracle of the Void from a copy of the forum saved in October 2015, so pages it didn't save are missing. Players' names are left out; the rules officials are named. Rulings are as they stood on these dates; later rulings, the rulebooks and the Rules Archive may differ.
A player, 7 April 2015
Regarding the previous ruling given this:
http://www.alderac.com/forum/viewtopic.php?f=59&t=113136&p=1463006&hilit=iron+armor#p1463006
The current rules on cavalry are:
"Absent Engage: Target your unbowed Personality in a Cavalry unit at any location. Move him to the current battlefield."
Noting that you cannot use the Cavalry absent engage with a non-cavalry unit: wouldn't the cavalry keyword give you the ability to use cavalry thus making Iron Armor stop the Cavalry Absent engage from a unit with the Iron Armor equipped?
Alex Jones (rules official), 7 April 2015
Regarding the previous ruling given this:
http://www.alderac.com/forum/viewtopic.php?f=59&t=113136&p=1463006&hilit=iron+armor#p1463006
The current rules on cavalry are:
"Absent Engage: Target your unbowed Personality in a Cavalry unit at any location. Move him to the current battlefield."
Noting that you cannot use the Cavalry absent engage with a non-cavalry unit: wouldn't the cavalry keyword give you the ability to use cavalry thus making Iron Armor stop the Cavalry Absent engage from a unit with the Iron Armor equipped?
The Cavalry Engage Player Ability is an ability in the Rulebook: it is not, as you suggest, "an ability granted by the Cavalry keyword".
Using the ability creates rulebook effects, not card effects.