They did say they did the run in June, to get the short nights and didn't use the radio. Wonder what the radio does to mpg? How much petrol it uses to run it? I never use mine if I am in the car myself, but my wife likes it on when we do our weekend run.
They also said the wind was from the south, so they must have waited for that too.
If the car was not prepared by the dealer I bet the tyres were pumped up to maximum safe pressure and the spare wheel, jack, suitcases etc were all in the van.
I'll have to have a look and see what Guinness World Records requires for the record to stand.