Yea but they had LOADS of Euro Fiestas in the US runnnig up to its laucnh which is about when that was revealed when they where touring them about.
Also theirs no way they could have the power of an engine in the Fiesta that would require an Intercooler...it simple wouldnt be able to handle that amount in such a small chassis and being so light.
They only had 5 door euro spec fiestas being driven as promotional cars. That's what makes it appear a genuine ford test mule IMO and not a tuners effort, and I doubt any of the US tuners would bother importing a car over from Europe to modify. Ford were probably trying to test it on the roads away from the UK etc where it probably would have attracted alot of attention, with the UK being the top hot hatch market.
And of course they could fit an engine in the fiesta which requires an intercooler, the corsa vxr has one and that's 1.6 turbo like the fiesta st is rumoured to be.