Kelly Holmes HRM: Help please?

Does anyone else have this? Is it accurate?

I ask because I have one and I've put in all my stats etc and today I did some running around and football (soccer) practice and after an hour and a half it said I'd burnt 1138kcal!! I'm 87.5kg, and 173cm (13 stone 11/193lbs and 5'8") and I wasn't pushing myself that much. Was running for the ball and kicking etc - just feels like it's way out and wondered if anyone had any ideas?

Thanks guys