Could he? Certainly he could see the RV coming up on the right, but I've seen that (usually a car) and the upcoming vehicle would realize he wouldn't make it and slowed down. From what's in the video that's what I'd have thought until the last moment when the idiot started moving into the left lane. So reaction time, disbelief, could have caused a slight delay in the truck's reaction.
And the truck driver WAS slowing before contact was made, as well as pulling over to the shoulder to try to avoid the idiot. Had he gone any further to the left he'd have been the one jackknifing, flipping over or worse.
Note that the extreme wide angle lenses on those dash cams distort the perspective and sense of motion -- pay attention to the time after the RV hit the truck until the truck was stopped -- when do you first realize the truck is slowing rapidly?