I really cannot comment on that. My friend I believe has the regular ~250 mile, or so, range Model X, so perhaps your brother-in-law has a longer range, but that still won't explain 3 times vs 1. So, don't know..

Edit: Now self-doubt is creeping in and I wonder if they had gone to Palm Springs and not just LA. The conversation was over a year ago.. Will that result in 3 charges each way? I've never driven to Palm Springs, so not sure if there is another mountain pass in that direction or not.

WLTP spec ranges favors city driving, in which Tesla has an edge because of the really aggressive recuperation braking. It also factors in highway driving at 90km/h IIRC, which no normal human being drives at. Highway it's actually not anywhere "light-years ahead" from other serious EV attempts like Taycan which does similar Autobahn range with wider tires than a model S.

If it's bothering you that much, might as well ask your friend again.