The former Swindon Town boss is well known for his fiery antics on the touchline, demonstrating them during the Black Cats' 3-0 victory over arch rivals Newcastle United last weekend.
"Inside the dressing room and on the training ground it is totally different to what you see on the pitch," Goal.com quotes Mignolet as saying.
"When you are winning or have won a game at Newcastle all the emotions come out, that's normal and his celebrations showed his temperament. But inside the dressing room he makes sure everybody knows what their job is."
Sunderland will continue their campaign for Premier League survival with a home fixture against Everton on Saturday.