After doing collision damage to a station guard (or it ramming into me, as happened in this case) followed by using a repair module to repair the guard's damage, it becomes hostile and all station guards in the sector attack (no strike force is deployed).

If the guard gets damaged by running into a roid or something (apart from colliding with me) then it does not attack when repaired.

I'm pretty sure both the collision and repair occurred in the NFZ, but I have no idea if the NFZ has an impact or not.