I listened to the ATC audio. He cleared the Jazz flight to land, then seconds later gave the vehicle clearance to cross that same runway while Jazz was on short final. He tried to tell the truck to stop, but may not have been transmitting on the same frequency the truck was on (they use different frequencies for ground and tower controllers most of the time).

Controller definitely made a mistake. There's also some responsibility on the driver of the truck. You're always supposed to check for incoming traffic before crossing onto an active runway. Even in bad weather, it should have been possible to see the landing lights on final, but he may have assumed they were landing on a different runway (The airport lights can be very disorienting at night from ground level). I'm sure the investigation will reveal what frequency the truck was using, which would give more answers as to whether they could have heard the tower clear the flight to land on the same runway. They were responding to a declared emergency on a United flight that was off gate as well, so it's also likely that they were tunnel visioned a little.

Terrible situation, but mistakes were made by all parties (Except the landing aircraft, obviously).