It's a good mix of blame, but I'd say the driver in the end. Doing a U-turn like that, you want to make sure there's no one in your way in either direction, and he didn't seem to slow down long enough to check both. That being said the biker was very slow to recognize the truck was stopping and pulling off to the side a bit, which definitely would've made my Spidey-sense go off. He didn't get the brakes til the last second.