the bars onside are to point out which hacks being used ie green no hacks and pink is fully paid up hacks from Activision
The bars are there to show if the player is on the game with a group or clan they are colour coded to show the differant groups say if there were two groups of 3 friends / clan members you should be able to see two sets of 3 players with differant colour bars . Ufn there is a problem with codeing in the game that gives a false reading so the player in the screan shot you posted is on there own but the game marks them out as joined on you . There is no hack its just bad codeing .
If you see a number of players with a colour bar next to them they are in a clan/group playing together you can get 3 or 4 differant groups in a game so you will see 3 or 4 differant colour bars to denote the group . As for the lone player with the bar i used to think it was just bad codeing from the game such is the amount of bigs in infinate warfare that is proberly the reason but in a longshot it could also be the marker for the player who is game host i suppose .actualy got to speak to a game ambasodor about it and they did not know either .