Well since the whole Gunslinger thing is fit for an Erron Black crossover, it could just be a spike nade that covers an area on the ground and all zeds moving through there are slowed down. Maybe even damage them.
There's an idea for a Gunslinger nade that's not just a frag/HE mixup.
With that said, I'm NOT bashing at the current grenade, I quite like it. Looking forward to playing it, though at this point I have literally zero hype for any new content. I'm just joining the conversation about the 10 different nades.