You might note that any time someone gets knocked over the player death is listed as having been suicide. In these mini games there hasn’t ever been a distinction between if I throw myself off a ledge and die or if another player makes it happen.
At the same time though, you do get a “you got a player kill” pop-up message, so at some point the game does consider that you get credit for it, it just doesn’t count towards the achievement.
This is a real problem. I had one situation the other night where me and another blue were shooting at a red with a crystal, and it was obvious we were going to kill him in about five seconds and very little could have changed that, so he just threw himself over a cliff to “steal” the kill from us.
Ideally, if a player falls off a cliff, by any means, then anyone who has damaged him prior to that should get kill credit. Any ability that knocked people off of cliffs should count towards that, since they all do at least a little damage on the attack itself.