I believe the confusion stems from available thrust, which impacts wind resistance, vs. maximum speed which is controlled by the FC. Unless I'm mistaken, the days of setting groundspeed records flying downwind with DJI drones is long past, as top speed is regulated by the FC based on GPS ground speed.
So it's entirely possible to have a drone with top speed limited based on non-technical factors (like product family), while having better wind resistance because of more powerful motors.
This is why the
mini 2 is only 2m/s faster than the
mini 1 in Normal, but has much much better wind resistance.
Ironically, the wind resistance spec is a better performance comparison between DJI drones than the max speed. In the former case, the aircraft is using up almost all available power to make ground progress flying upwind; at max speed it probably isn't – under most mildly breezy or calm circumstances.
As for how DJI measures wind resistance, they don't tell us. But they're good engineers. I expect they have a consistent, repeatable test environment for this.
I disagree with
@Meta4... Top speed specs are what are relatively meaningless as a performance metric. All they tell you is what speed DJI has configured as a limit. The fact that max speed is different for C, N, S modes makes this case. All you're gaining insight into is what DJI has set the max speed to.