Randomly getting kill effects without killing anything

As a Berserker with a Showstopper mace, I have two effects that have a chance of happening when I kill an enemy: the Rampage skill, and Meteor Strike that has a 10% of happening when I skill an enemy with Showstopper.
The weird thing is, they've been randomly triggering. I'll be just walking through a dungeon, minding my own business, when suddenly a meteor falls from the sky and hits an area near me. I've also have Rampage randomly trigger without any obvious cause.
This is not caused by my pet or a summon killing something. It's happened in cases where I have no summons active, and can see what my pet has done for the last few seconds.
Is this a bug? Am I missing something?
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