What’s included in the "longest kill streak" on the leaderboard?

I used to think it was gun kills only however today I started a game with 35 straight kills before dying, quite a few of those kills came from my helicopters. I wanted to see how close I was to my first MOAB but when I clicked on the leaderboard it displayed my new longest kill streak at 28. I'm confused now what exactly gets included into the leaderboard longest kill steak.