Since the introduction of character stats in the main menu, I don’t think they’ve ever been correct for me. It often says I’ve killed people when I haven’t, or vice versa.
I’ve had a character who had been alive for days, that, according to the stats, had only been alive 40 minutes, and killed a handful of zombies.
Travel a certain distance in game, kill a specific number of zombies/players, and make a note of the numbers.
Exit to the menu to see if the stats match up.
I have the same issue and to add more details I think it's pulling back stats from the same server but it might be the person who's been in the map the longest. When this situation occurred, my stats where correct.
Related bugs describing the same fault;
https://feedback.bistudio.com/T146712
https://feedback.bistudio.com/T144891
https://feedback.bistudio.com/T139477
https://feedback.bistudio.com/T141374