You know yourself that more has been accomplished than the apps says, so don't worry about it. Besides, despite their promises, modern technology quite often fails to calibrate correctly.
Equally, when attempting to lose weight, what really matters is the intensity of the activities, since the more strenuous the activity, the greater the uptake of glucose and fat.
You and I both know that your kettlebell workout wasn't at all easy, since it'll have kept working heart rate close to its aerobic/anaerobic threshold throughout the 30 minutes, while hurting every muscle in the process, but that's good, since that's how muscles grow and adapt, thus, increasing resting metabolism.
As such, I do hope you've taken on protein and carbohydrate, to help replenish and repair, particularly since insulin sensitivity is incredibly high immediately after strenuous exercise.
In all honesty, the 30 minute kettle bell work out probably would have sufficed, but you've gone above and beyond, so your overall calorie expenditure will be far higher than the app states.
Provided you're continuing to maintain a calorie deficit alongside regular exercise, you don't need to fixate so much upon how many calories are being burned.
Instead, focus upon how much the muscles may burn, as lactic acid builds, and how hard and quickly you may breathe throughout.
In essence, the more it hurts while attempting to sustain the same level of intensity, the greater overall calorie expenditure will be.
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