Was this guy right for being angry?

I was in a taxi, and I saw a girl got in the front seat with the driver. They gave a kiss which showed that they were in a relationship. I then saw the guy take the girls cell phone, looked at it and then got really angry….yelled something and slammed the phone on the floor. It had some loud music in the car so I could not hear what they were saying My guess is that he probably saw a text that pointed that the girl was cheating on him. My question is do you think that the guy was wrong for looking into her cell phone in the first place? Wasn’t that kind of nosy?