Do you program your weight & age into the treadmill? Mine is a cheapy and doesn't store that information, nor does it record my HR BPM. Your calories burned are dependent on all that stuff, so if it's not brought in to the calculation on the treadmill, it's only giving a guess based probably on the average person.
I use a HR Monitor too, but I don't use the calories from that one either, I use a calculation that takes my age, weight and VO2 max information. That's your most accurate. I don't know if it's actually possible to really know exactly how many calories you've burned, I just know that my treadmill is WAY off.
The Workout Manager is basing it off of an intensity that you put in there too. Are you putting in the speed of your walk? Then there's that whole MET number, which I have no idea how to manipulate accurately.
