I have a hunch that it's overestimating because you wave your arms around a lot, but 360 seems like an underestimate. Average heart rate in 70% to 80% range, and I'll have higher than average calorie expenditure because I'm overweight.

EDIT - did a comparison against Runner's World's calorie burn calculator, and the calories/hour burn rate lines up with a leisurely 11:30 minutes/mile pace based on my weight.

It honestly seems about right.