Ray I agree with your quote. Joy, Music and even noise is essential for Christians. I could not but notice that during the World Day Masses, while there was silence at the must sacred moments there was clapping and cheering at other times.
You question
Is all this singing and dancing and rousing celebration indicative of deep faith, OR is it simply the exuberance of youth.
is hard to answer at the moment. If in the future these young people commit themselves to their religion by becoming religious or even goint to church than there is an indication of Faith.
All I can say at the moment is that the young people I seem and heard do testify that they are here because of their faith. They are proud to be Catholic amongst so many fellow believers from so many countries.
They have had rock concerts but their have been no arrest for bad behaviour which is useful for such events.At the moment I will give them the benefit of the doubt.
Only time will tell.