That's how things should be, justice among players, not GM and devs!
Not if gridcamper exploits map loading delay. While "normal" PK is a valid way to play the game and should be "punished" by APKs, gridcamping goes beyond the whole "PK - APK" stuff, as it is just cheating.
However, according to Chamo these dudes were just legally camping, not gridcamping, so if that is true, then yeah, justice among players was the right solution.