You chose a Great Song...

[cattj]

.. says Simon Cowell to the guy on Britains Got Talent playing a saxophone solo.

I heard no singing.

Am I the only one who noticed this?

I've heard him say it in multiple BGT and XF shows over the last few years.

What word would you use instead of song?

"Piece of music"?

Piece.

But it can be a song without singing anyway.