It's like tk says
People can use a spoof that makes it appear like their name is "disgruntled" but it's not really them, it's a hack program.
If you type /ping, the server will return you the real name of the player in the game with you. We always ask that you type /ping and take a ss when you want to report cheaters. That's the regular procedure because unfortunately people "spoof" others' names sometimes...