I wonder if that's because of the Community Bounties they run? I forget if I was in the base game or playing The Following DLC but I joined that Community Bounties thing one time which is where the whole community's kills are lumped together and it seemed like after that they just kept putting my kills into the Community totals and counting them towards the Community goal that day.
Never had any problems from using the Trainer tho and I played the game quite awhile. That was a coupla months ago though so that could have changed. Joining Community Bounties is probably a bad idea if using a trainer.
I never play MP. I played SP in Dying Light and The Following while using the CH trainer and loved it. I never had any problems bro.