I have a polar HRM that is not near as fancy. It's meant more for fitness classes and such, not biking. Here are my stats from today:

Distance: 24 miles
Total time: 1h:42m (incl stops)
Terrain: sort of flat, slight hills
Avg HR: 141
Avg speed: 15 mph +/-
Cal burned: 750

About me: 33yo, 5'-7", 130 lbs.

To me, your calories seem very low for 4+ hrs of riding but what do I know?! I often wonder the accuracy of HRM anyway.