Electric motors work well even at high altitudes. So you can launch that drone at 18,000 and it will climb to 19,000. But launched from sea level? There's a difference between "ceiling" and climb possible on the stored energy. That model has a claimed flight time of up to 30 minutes. Can it climb continuously at about 20 knots vertical speed? That's what it would take to climb to FL250 and then come back down at a similar rate, all within 30 minutes.

Good point. As mentioned, I am not an expert on drones. Perhaps it was a run-way and it climbed until the batteries were dead with no plan to fly back down? The DJI apparently has a climb rate of 4 m/s x 60s/min x 30 min is 7,200 meters (23,600 ft)? Elevation in that area is ~2000 ft, so if it could climb for 30 min at the advertised climb rate, that would be 25,600 ft? There is apparently more powerful drones, one of which claims a climb rate of 40 m/s or (140 km/hr). The website doesn't say how long they can climb at that rate.