I think it has to be KPH aswell. Top gear quoted it did 0-60mph in 2.5 seconds, it does 0-100 in that vid in around that. It doesnt seem to travel that far either for doing 210mph. At that speed the car would cover 3.5 miles every minute - which in turn works out at 0.058 miles every second. That converts to 93.8 metres. It sure doesnt look as if it covers the length of a football pitch in the time when he does 210.
Bugatti boast the top speed as in excess of 400kph aswell so imagine this will be in KPH aswell.
Edit: Just found this.
http://www.letstorquebhp.com/featured/feature02.asp
Think that proves its definately KPH.