I would assume any action done after combat is engaged. (you see the crossed swords appear on your character) would put you on the threat table.
this is a big concern with world dragons and failure to leash/reset.. anyone, even blessing of wisdom on the person. will put that player on the mob's threat table. even if it is 0, you're stuck on it forever until you die or disappear off of the threat table (feign death/vanish).
so yes.. if a warrior pulls a mob.. and you're in combat as well as the warrior who pulled. if you did any action like PWS or renew. you're on that mob's threat table. it will be 0 since shielding gives 0 threat, but you're on it.
think of it as a link in the chain.. if a warrior butt pulls something and he gets into combat. if I do ANYTHING to that warrior even shielding him. I am aggroed to that mob now and in combat (0 threat on the mob's threat table that the warrior was on).
so whatever mob the player is aggroed on, if you touch that person with any ability, it will throw you into combat and on the mob's threat table too.
world bosses is the biggest example of failure to understand mob threat tables and such. (china running lethon around hinterlands 1500 yrds and such because people keep getting added to the threat table by proximity threat to the mob or touching a player in combat with the mob).
there is a bug on Nost with blessing of wisdom mana ticks forcing the paladin who casted it onto the player's threat table.
if pally #1 blessing of wisdoms me and is in cenarion hold selling stuff. I go to the twilight camp and agro a giant worm on the way.. if blessing of wisdom mp5 tick happened.. that big worm will run 100x speed towards that pally #1 sitting in cenarion hold.
so pallies.. BE VERY CAREFUL OF BLESSING OF WISDOM!.
unless you wanna be perma combat bugged in the world.
instances work differently.
when a mob is aggroed, everyone inside the instance is put into combat.
however, if you're not within agro range(proximity) of the mob when the idiot pulled it.. you should be safe from it.(blizzlike function). however, if you're in proximity of the mob you will be thrown in its threat table.
I believe nost has it working incorrectly with threat tables inside an instance. (I could be wrong) but I don't recall the entire instance pulling to your group when someone aggroes a mob at the entrance and so on back in 2006/07. if its BWL and an idiot pulls a whelp running in.. expect 150 whelps to greet your raid by chromaggus and so on.

#nostlike