I know nothing of Pinarellos but it looks as if it might be legit. If the top tube were not curved the headtube would become more perpendicular and the wheel would hit the frame. The fork does not seem bent. A Duckduckgo search (pinarello curved top tube) found several examples including this one: Vintage Pinarello Treviso Italia Bike Frame Fork Ferrari Seat Curved Frame | eBay and an ad without pictures for a Prologo.