the latter number is the more accurate, so your explanation of revising the estimate does make sense.So that second reading is just 10 minutes after the first. Did it settle down after that or increase again without additional exercise?
My guess is the "flights climbed" is an estimate and uses a combination of barometric sensor and possibly GPS data.
If ambient barometric pressure is changing quickly it could or likely will screw up the estimates. The phone could also be recalibrating and correcting itself over that period.
Which number is the better estimate in your opinion?