Si is not required here, it just puts more emphasis on how varied the songs were. The English text doesn't give a clue that you'd need to have si or tellment as a "booster". 

But remember: there is no "marked wrong". You're only shown the differences between your answer to the preferred answer. Those are not necessarily mistakes. It's up to you to see if they really are mistakes or just different ways to say the same thing.

Thanks, I'm not too hung up on the marking, just checking in case I'm missing a subtle difference between french and english ways of expression.