Aside from all the other things wrong with that paragraph, higher heart rate does not necessarily mean more calories burned. Heart rate is just an indicator that heart rate monitors use to estimate calories, it is not itself a cause of the burning of the calories. There are many factors that affect how much oxygen is required for metabolism (oxidation rates are different depending on what is being burned), as well as how much oxygen is being transported by your blood. HR calorie estimation is based on statistical models and is not even remotely a direct measurement of anything.
Agree. Doing one-legged drills on a bike can get your HR super-high because your body is attempting to pump more blood throughout the entire body just to get some to that fatiguing leg, but you're likely burning less calories than you would had you been doing two-legged cycling and engaging both large glutes/quads + heart. The increased calorie burn by the heart won't be equivalent to the muscular calorie burn.
I'm currently really struggling with this phenomena in swimming - I've got good bike/run cardio but I get in the pool and my HR goes through the roof at slow paces even because the capillaries in my arms just aren't up to snuff.
Back on subject, ride whatever you can maintain - it's trial and error. Guys who have powerful quads might feel more comfortable in bigger gears, whereas light guys with great cardio and less power (I ride with some great runners who don't have much bike power) may be in smaller gears and faster cadence. I think I have more of a power/sprinter physiology and as such do ride bigger gears, but once the climb gets long or very steep, I'll be grannying it all the way up as well.