"Things You Wouldn't Know If We Didn't Blog Intermittently."
Hmmm. I had heard about this story and always thought it was phenomenal. But now that I see the clip and read the Youtube comments, I'm tempted to agree that this might be staged. First off, it's unlikely that the pianist and conductor would have mics on them allowing us to hear them speak (although some parts may have been added in postproduction). Secondly and more importantly: there must have been rehearsals, so how could they not have noticed this way ahead of the official performance?
I totally reject your Debby Downer negativity. This was not a major concert requiring rehearsals - it was a lunchtime "music in the park" kind of event. And he tells her 'U speelde dat het afgelopen seizoen' = "you played that last season", so they had done this together before. And there are plenty of audio feeds for symphony performances being recorded without a need to "mike up" the pianist and conductor.
Haha, hey, don't worry I'm just being analytical, and I may be wrong. It's a great story, whether it's true or not.