I took a look at RY's KOMs on Strava and noticed this run. Sorry if you've covered this before...
(Firstly, its a bit odd that he has the course record for a segment during this run, but is one of only two people to ever run the segment, the other one being the other Rob Young account. Weird but not suspicious.)
This run is a classic example of erratic walk/run pace and zig-zag across the road, quickly switching to much faster pace and a smooth GPS line. Those speed point changes are matched by the GPS track showing a little swirl, that others have suggested is RY entering or leaving the van. This is up a pretty steep elevation too.
2.4km - he gets into the van
9.3km - he gets into the van again
Oh and guess what, this is from the evening of 18th May, the day they got stuck in the sand...
I think that one's legit. He's established he can run 6-7 minute pace for a mile or so, but almost always takes breaks afterwards. On Strava, the signature is a 6-8 minute per mile "plateau" for a mile and then a few minutes of walking (15-minute pace).