The actual average driving speed was even higher, the car must have refueled at least once ( no way they get a reach of 460km at that speed with one filling) and also the non highway parts of start/end drag the average down quickly. My guess is at +280kmh (175mph) driving speed most of the time on the highway to make up for that. In times of covid and partial lockdowns it's not unusual to have empty highways (depending on the time window this happened). In germany you can definitely average 230km/h (140mph) when the Autobahn is empty, eg. at night. Conditions need to be perfect though (almost no traffic, weather, powerful car and a fit driver). Maybe they changed seats after refilling.