I noticed this when I’m playing as Kait (I almost haven’t play as another character for now) and I joined to a custom horde (On master).
First, I was on Icebound (wave 37+), host and the rest were spamming JD, Del and Fahz laugh, so I wanted to do it too. While I was trying to do the emote, I accidentally move 1 barrier. After that, some barriers kills were credited to me.
Second time, was on Forge. Every barrier kill hasn’t the name of the engineer (I suppose that original engineer left at some time), but sometimes I got some kills.
Is something like the kills on versus? Maybe I did a lot of damage to one enemy and he died for barrier damage but the game credited me the kill? Problem is that I didn’t saw that for the rest of the team.