Performers bowing when there are people behind them

Factual Questions
1

I attended a concert tonight at the new Walt Disney Concert Hall in L.A.

In that venue, they sell seats behind where the performers are located.

At tonight’s concert, the performers always bowed to the front of the arena, but every so often would stop and turn briefly and nod to the people in the back.

Then at the very end of the concert, they made a full bow to the people in the back.

Is there any particular etiquette that performers follow when there is a crowd that surrounds them on all sides?

2

No, there is no etiquette other than making sure that every performer bows to every audience member, however they are each arranged.