Looking through the grimoire I realized that the Warlock card has a section labeled Crucible Kills as Warlock. I currently have 532/1000. I've never played as Warlock at any point. The only thing I can think of is if Assists are getting counted. For example a Warlock on my teammate and I are shooting at an enemy, the warlock gets the kill credit and I get the assist credit and the grimoire counts that as a Crucible Kill as a Warlock. I'm not sure if this is working as intended or not.