Those are all guesses. They're different because they use different algorithms. There is no direct correlation between HR and calorie consumption. People's HR varies for the same power output (calorie consumption). Two riders who are in the same shape, weight and age, producing the same power, may have HRs that are 20 bpm different.
The only ways to measure instead of guess calorie consumption is to measure power output, or to measure something that indicates metabolism, such as oxygen (air) consumption or CO2 exhalation (and then subtract basal metabolism). The latter is what's used in lab studies but you can't take that equipment out on the road, and you wouldn't want to breathe through a mask for 2.5 hours if you could. You can measure power with a power meter, and then make a guess about riding efficiency in order to estimate calories. Efficiency ranges from about 17-23%. Most people assume the higher end because then the conversion from kJ to calories works out so that the number of kJ equals the number of calories. Unless you're at the high end of efficiency this number wind up being slightly low.
I would ignore the calorie guesses entirely, or use the lowest one you can find and realize that it's not accurate and is probably still too high. 1580 cal for a 2:26 ride at 13 mph with not much climbing sounds low, unless perhaps you're over 200 lbs.