What do the bars mean next to the persons level?
Once you reach level 50, your level resets to 1 and you become Echelon 1, level 1.
The player in your screenshot has reached Echelon 2... so he's much more experienced than his mere number 14 (level 50 + 50 + 14).
See https://bethesda.net/#en/events/game/doom-player-progression-and-customization/2016/04/14/105