It could be either. He purposely sped up (knowing how fast a pace car can go, around a corner and in the wet!), moved to the right protecting his rear AND narrow the angle as you are not allowed to overtake. He was fully aware that something was going to happen! Ruthless tactic that one day will come back and haunt him.
I struggle to believe that he did not know before hand what the potential consequences of driving in that way are. He is a very well paid professional who spends hours very day thinking of every consequence to every situation. Their is no way that he had not run over a situation like that in his mind before.
Using rain, visibility etc as excuses/justification simply make him appear amateurish, which as we have seen this season he is anything but. Oh no he knew exactly what he was doing. He is a professional. My opinion.