blooper alert

Yeah I kind of noticed this as well. But what I think happened was that whilst they were shooting, they do a few retakes. And I think during the editing process they just cut and merge the material that they have, and that is what leads to this blooper. So in one shoot he must have held her left hand, and then her right. Also if the editors do realise the mistake they can't and won't go back to shoot the whole scene again. I'm just assuming!