No, people are confused about this because although Cena is a white meat babyface, people hate him so they boo him like a heel. So, I will illustrate to you what happened. Cena was the face against the heel Rollins.
Stewart comes to the ring and turns heel by hitting the Face with a chair. Cena confronts the heel and gives him the punishment he deserves. It is quite simple, however, its complicated by the fact that Cena is booed as a face and Stewart is cheered as a heel.