It's all to do with what we understand by performance as a public event.

with 后面宾语从句的结构是：

understand sth. as ...， (sth. 由 what 充当）： 把...理解为...

by performance 的意思是： 通过公共活动的表现。

by 的意思是： 就…而论; 以…称呼方式; 以…的名义; 凭着。英文意思是 through the means of。

意思跟下句的 by 应该是同一种用法：

What do you mean by a good horse? 

你所谓的好马是什么意思呢？