个人觉得楼主理解有误.
about可以表示“关于...”,另外on也有这种用法.
by也有“关于...”的意思,但是此句的by并不是这个用法.
by表示“关于...”时,更准确翻译为“就...而论”.
如：He is a doctor by profession.就职业而言,他是一个医生.
She is French by birth,but has British nationality.他生为法国人,但国籍属于英国.
个人觉得此句中的by还是表示被动语态中的“被...”之意.
即：I was also looking for something by Confucius.
= I was also looking for something (said/done) by Confucius.
我也在寻找（被/由）孔子（说的/做的）某些话/某些事.
再如：I like books by Mo Yan.
= I like books (written) by Mo Yan.
我喜欢莫言写的书.
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