How is this possible? Well, Saab have always been pathologically insane about safety. In an age way before people were so conscious about crash tests and such things, the Swedes designed some of the most structurally rigid cars on sale.
General Motors often complained that their Swedish engineers never asked what they were supposed to. Instead of simply restyling the Opel Vectra body with different headlights and bumpers, they changed just about everything to make it strong in a crash. So that's why a car that entered production over a decade ago is made of the right stuff and the supercar… isn't.
There's also the fact that carbon fiber tends to shatter on impact to dissipate force and that the heavier Saab has more momentum, but that's kind of insignificant in this type of urban crash. What isn't insignificant is the amount of damage sustained by the 650S, which pretty much needs a new front end from the windshield forwards.
What's interesting is that at about the 1-minute mark in the video, there's another McLaren 650S Spider visible in the background. Now, the last time we checked, the only green model in Britain belongs to supercar spotter Shmee150, who previously owned a 12C and an Audi R8.