I just watched that and I think the actor probably
can play the violin but certainly wasn't playing that piece - at one point he was bowing the E string when the D string was sounding
He could do a little vibrato though which isn't easy so he's probably played the violin in real life.
Also, I thought actors were not allowed to play 'on film' even if they can play an instrument, because a professional musician
has to record the soundtrack.. something to do with Intellectual Property Rights?