Since it was supposed to be a concert, it kind of added to the concert atmosphere.
I think that for some people, jukebox musicals do seem like concerts - but in their entirety. So they behave more like they would at a concert. I can't speak to the behavior mentioned above at the Play That Goes Wrong. But for jukebox musicals, there really may be the mistaken impression that it can be treated more like a concert.
I saw a production of A Chorus Line back that the beginning of August. After the tap sequence and where SPOILERS
Paul falls and is taken off to the hospital (does anyone out here not know this?)
When the music starts up again, it's the tune of "Who am I anyway/ Am I my resume" etc - and a guy sitting near me started to hum along. Well, nice for him, I suppose...