In that case, if a(-ny kind of) faction is trying to take control of a Town during the not so crowded hours, usually referred to as "night time" by Europeans, because they don't want to take chances in a fight, but members of an "APK" faction just happen to be online and try to ruin their operation, would you say the attackers are PKing?
(I am asking without any intention to troll, flame, etc. - It's just that your vision is interesting even if I don't really share it, as I think it has to do with players' behaviour in specific contexts)
Let's put it this way, town control is designed for PVP, so if you're there, and you don't want/expect to deal with being shot at, you're just not smart. A town control fight is the ONLY true pvp in this game, where there is an expectation of a fight, the chance for a challenge, and even a reward for it. Anywhere else it's just kids playing with an ant hill and a magnifying glass.
In truth the difference between a pvp'r and pk'r is just simply semantics. PvP is the Action, where PK is the person 'behind' the action. And yes in the Fallout Universe, it really is a PvP sorta place, but no matter how you make it, the games that work have some rules. Whether forced by programing, smart people realizing that killing everywhere anytime doesn't work, or just dumb luck.
(Look at it this way, do you REALLY think you would have played Fallout 1, 2, Tactics -maybe 3- If all you had to look forward to was getting killed before the first quest even starts, and having to reload?) Really?