It only gets slightly warm because it has thermal management and that won’t let the light get that hot. 5A 6A for 1800 or 2000 lumen seems in the ballpark. Different LEDs have different efficiency.
Don’t know what light they use and I am not certain how the electronics inside the light will change the output vs the chart linked above. Nearly certain the output would have to be be lower than the chart but not sure how much. The specs for the light pretty much confirm that your friend is not walking around at 1800 lumen the whole time. They list a minimum run time of one hour with a 3500 mAh battery. That would be an average of 3.5 Amps. Looks like you coud get maybe 1400 lumen from that but given the fact that it starts at 1800 Lumen it would be drawing more for some time and therefore must settle down lower than 3.5A. Hopefully someone who understands how an actual flashlight is different from that chart can add to this.