All the ex-drivers on Eurosport attributed blame to the Ferrari. He knew he was there (as he said himself, and even before that they said he should have known from checking his mirrors and the sound of its engine), it’s apparently a typical passing spot on slower cars, he left plenty of room up the inside inviting the pass, then pulled across without warning. If he couldn’t judge the distance in the daytime, it’s a relief he didn’t get a chance to compete at night- not that he could have caused any worse a crash anyway I suppose.
Regarding the fin, once the car has started tipping and air is underneath, surely all the fin does is resist the airflow in a way that would exacerbate the tipping. It way well be preventative up until then, but surely it acts as a sail and makes it pitch more once it already starts.