我的理解是在这里conviced是用被动形式表示主动的含义.并非是由别人所劝服的
比如说
I am convinced that it will be fine tomorrow
我相信明天会天晴的
类似这种被动形式表示主动含义的还有prepared,opposed等动词
The teacher is satisfied with what he said.
师对他所说的感到满意.
We are opposed to unjust wars.
我们反对非正义的战争.
We are prepared to accept his proposal.
我们准备采纳他的建议.
He was tired with playing all day.
玩了一整天他感到很疲倦了.
这么说,不知你是否还有疑问?