Of course he didn't open the throttles knowing the RW was occupied. And therein lies the problem and challenge for us all. The KLM PIC was sure he was right. Until we get to a stage when our own certainties can be readily turned into a "check again"uncertainty as long as one crew member has any doubt, we'll get nowhere.
Its also true that any crew member (such as F/E Schreuder) who lets his own doubt be over-ruled by another crew member's certainty, has let the whole team down and ultimately the passengers.