I doubt that he would be writing specifically for peers of Wooster, not least because he himself was not a peer of Wooster.
Wodehouse was more closely a peer of Mike Jackson from the Psmith books. Reduction in family circumstances robbed Wodehouse of a career at Oxford, sending him instead to the Hong-Kong and Shanghai Bank closely mirroring the reduced ...
Break out in the dictionary means:
to develop or emerge with suddenness or force Merriam-Webster
Some examples given are the fire broke out or the riot broke out, meaning, suddenly began.
So in this case, 'the orchestra broke out' means 'suddenly started playing'.