My guess is that they had an inversion layer, tropospheric duct, or other enhancement condition. 43km is a long way on 0.02 watts.
Of course you’d have a little problem with the battery :-)
Of course, the VTX is usually a different matter..
[0]https://www.expresslrs.org [1]https://www.expresslrs.org/2.0/info/long-range/