Well, the Al Ahram report is just a teensy bit fanciful. Formula One it most certainly was not! The Cisitalia D46 - more correctly the type 201, but D46 has become ingrained ('Dusio 46') - had only made its debut in September 1946 in a race in Milan and far from 'racing all around the Mediterranean' only one had competed thereafter - in the Penya Rhin GP in Spain.
Dusio's original idea was indeed an all-star one-make series, but - as mentioned - the Cairo race was a financial disaster and the planned next race in Alexandria was cancelled - as were plans to fly some of the cars to South America afterwards - and the whole thing went tits up. Although the Cisitalias were very successful in Italian national racing over the next couple of seasons.
Nuvolari of course didn't drive a D46 in the 1947 Mille Miglia - it was a type 202 sports car.
Just for fun, I did go round the circuit on Google Street View a while back! That tight corner seen on the film was - I suspect - the only really challenging bit.