People are taking the call in the US-Slovenia game as a single frame in an entire movie. In order to understand why Coulibali made the call, you have to understand how FIFA operates.
In the Argentina-Nigeria game, a goal was scored when an offensive player unfairly created space. FIFA then instructed the referees to become more vigilant during set pieces coming into the penalty area. Coulibali quickly scanned the ~5 areas of matchups and his vision was tunneled on Bocanegra and his matchup. When Edu broke free, Coulibali assumed that Bocanegra held the defender back to unfairly create that space. The whistle blew, then the ball was kicked into the net. No goal.
It is extremely difficult for those outside of the soccer community, and specifically the referee community, to completely grasp the entirety of the situation. I had a customer today ask why "#### referees from third world countries" are in the World Cup....only to remind him that the only American referees in South Africa had to buy tickets and sit with the rest of the spectators. Coulibali, while being no stranger to controversial decisions toward the end of matches, was one of 32 chosen to take charge of a match. He was chosen for a reason, one that does not include the taking of bribes or deliberately altering the outcome of the match.