One of them was strange UID range starting from 50000.
I thought it was a bug - you can't add that user from this UID range into friends list.
Also I thought this UID range was given to previous players who played alpha test, beta test, etc.

Bots.
Maybe someone already discovered this before, but anyway.
If you want to check who killed you, a bot or a real player - just press X button (it works when you are killed by an enemy and when the camera "zooms in" on the enemy, not afterwards) and UID will appear in the report window:



Or just click "REPORT" button from player list.



If it starts from 50000 - it's a bot.
If it starts from 100000 - it's a real player.

yea ik you can simply look at the players and see who is a bot and who is not lol