No.
You have discovered why a HRM is a Heart Rate Monitor, not a calorie burn measurer.
It's a formula, calculations, and estimate to get calories from HR. And several assumptions.
The correlation between HR and calorie burn is ONLY valid for steady-state aerobic (same HR no intervals up & down).
That limited range can be decent estimate of calorie burn depending on figures used in the formula - but even there the ends of the range (right above daily activity, right below going anaerobic) are inflated calorie burns.
HRmax is a rather major figure in the formulas - and it's totally estimated from 220-age. No gender specific, no consideration of having kept it high by exercising through the years, no inclusion of genetics, ect. The bell curve on that accuracy is wide, for women more chance being outside 10 bpm accuracy than being within.
Assumptions that unhealthy BMI means unfit, and healthy BMI means fit - which we probably all know many that are opposite.
So your HR increased from probably trying to cool the body - not aerobic exercise.
Therefore not valid use of HR-based calorie burn.
No you didn't burn that much.
The heart does not use that much extra energy to increase HR, beyond just the fact of beating.
If you can walk fast enough to get your HR up to say that same 128 without being dehydrated, overheated, stressed from prior hard workout, meds - now you know the level of intensity that matches the NEED for that HR to provide oxygen to oxidize fat and carbs to provide energy.
Now the formula would apply as possibly best case usage.
And the calorie burn could be decent estimate.
Great example to be aware of though, thinking now of people using hot tubs more in the fall, seeing that effect, and thinking they've found a great exercise replacement to burn more calories.
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