In the early 90s in NorCal, we used gank to mean "steal" or "snatch", and you can still find this definition online. I don't think it ever meant murder until it got used in PvP games.
Aren't these murders for stealing though, like don't you kill the people and they drop stuff. I don't remember the game but I know people used to sell in-game items of high value on eBay then stalk people for a bit and kill them to steal it back. One guy got mad about it and went and killed the people in real life.