So we're expected to take on faith that an inexperienced 'stunt runner' was able to beat the WR of an established, multi-day, 'elite level', ultra-runner all whilst admitting to having poor nutritional prep for the 'event'. Having poor physical health (losing 28 pounds in 7 days is not healthy), blisters, and was already behind the WR after day 1.
If I am honest, this sounds too good to be true. It is possible that they (Amy & Dave) went into the challenge with the firm belief that it was doable however, they probably realised after day 1 it was going to be much tougher than they ever thought. To me, their attempt was amateurish, poorly planned and poorly executed.
You're giving ultra runners way too much credit. An 'elite level' ultra runner is basically just a hobby jogger who moved up distance because there was too much competition as shorter distances, The reason these stunt runners can break these records is because the current record holders are just slow, less talented runners like them. It's not like they are out there breaking 27 for the 10K. These are cheap "records."