Is it really Steve McQueen's car?

No, it isn't McQueen's car. It's a replica of it. The Wiki for this movie links to the movie's production notes [PDF]:

The pièce de résistance of Arthur Shaw?s multimillion-dollar penthouse equaled a 1963 Ferrari 250 GT Lusso that was once owned by Steve McQueen. It provides the billionaire with lofty bragging rights. This highly coveted and priceless collectible is the crown jewel of Shaw?s home. To showcase it among his other treasures, Shaw had the car cautiously disassembled after its purchase and then reassembled in his penthouse apartment.

When it came to this aspect of the story line, the filmmakers became quite inventive. McQueen actually did own a Ferrari 250 GT Lusso, which venerable auction house Christie?s auctioned off in 2007 for $2.3 million. Several years later, that wise owner sold the car for a staggering $10 million.

The rare sports car (only 350 of the models were ever manufactured) easily sells for close to $1 million, so the practicality of buying one for the production was not an option. Frankly, it would never survive the rigors of filming. The next best plan was to reproduce it, so the production commissioned two replicas, both of which had different uses for filming.

Once the decision was made, a little creative license was taken with the final color of the vehicle. The McQueen original was custom painted a muted "marrone metallizzato," or metallic brown. "The King of Cool" chose the color to elude law enforcement when zooming up the Pacific Coast Highway. However, the filmmakers wanted a vibrant, eye-popping color that would leave an impression. After performing camera tests on three versions of authentic vintage Ferrari colors, the filmmakers decided on "amaranto," a brilliant red.

This is also confirmed to an extent on IMDb.