This is the first character with stun resistance made available to players, so they clarified it a bit. You do not have to fire the blue ability to trigger the stun resistance.
“Yes, this means you need this power for the stun resist to kick in.”
Seems fairly straight forward to me. It “kicks in” to the character build with the first blue cover, like any other passive. Maybe they could have avoided the colloquialism.
It is like any other Passive/Active. You need the cover for the passive to work, the AP is only for the active portion.. this is true on any passive/active power.
He won’t start spamming trap tiles until you have the first pink cover. That ability also has an active to fire but the passive will still occur each turn whenever possible.