1) Nature abhors a vacuum.
2) Any existing pressure differential creates a dynamic in which a 'high' will attempt to 'telegraph', 'communicate', with a 'low.'
3) The, what is typically considered, 'low' base pressure behind a vehicle, CAN be of higher pressure than elsewhere on a vehicle. An example would be a hatchback car with the hatch propped open, to allow the transport of an oversize item.
4) With the hatch open to base pressure, and a driver's side window rolled down, it's normal for engine exhaust to travel forwards through the cabin and asphyxiate the motorists with carbon monoxide, due to a low pressure caused by the A-Pillars.
5) A tunnel-effects ( ground-effects ) venturi , underneath and ahead of a diffuser, could certainly impart a suction peak ( that's what a venturi does ) sufficient enough to induce counter-flow beneath the Lamborghini. It's a physical imperative for this to happen. The orientation of the tufts would suggest that this is the case, with respect to this particular vehicle. Whether it agrees with a textbook or not.
Exceptio probat regulam. Just sayin'
