At that temperature I reckon the vinyl would have cracked if he'd have folded it down.
Reminds me of a bloke I met on an expedition to Antarctica who made a windsurfer to use on the ice. It was a like a big skateboard with ice skates instead of wheels, and it used a normal windsurfer type sail. First time he took it out for a sail it was probably -30C or thereabouts. The sail filled with wind and he took off like a rocket across the ice. It was all good until he tacked. As he flipped the sail around, the cloth had to bend the other way, and the clear plastic window in the sail shattered like glass.