The incident led to manager Steve Bruce calling his players a "bunch of "p*****s."
"John Mensah and Nedum Onuoha were two assertive players in the dressing room, not to mention aggressive," Mignolet told The Times.
"After one of them played a short return pass, the other decided to make amends and make him feel small at half-time. At least that was the intention.
"Our captain [Lee Cattermole] jumped in and Bruce was called from another room where he was with his coaching staff.
"Bruce said: 'Let them have a proper fight. If they want to fight, let them fight.' There was nothing more than a little pushing and pulling. Bruce said: 'See now. You are a bunch of p*ssies in the dressing room and on the field.'"