The evidence says he knew they were telling the truth. [/quote/ No, the evidence does not show that. You are bootstrapping from the jury's conviction.
You're saying his claim that he thought they were just joking should trump this.
No, I am saying that it is very hard to know what is in someone's mind.
I simply cast the same logic into another case where the act is either legal or criminal based on what the person believed.
No, you didn't apply the same logic, You constructed a poor model. Here is a better model. Suppose I say "I've come to the conclusion from all of your posts, that you know people are truly guilty when a jury convicts them", and I trot out 100s of examples from your posting history to support that claim. And 11 other posters chime in and agree, so that 12 people look at the evidence and they all agree that "LP knows people are truly guilty when a jury convicts them". According to your argument, those 12 people accurately know what is in your mind about this topic.
If "I thought they were joking" is a defense against providing resources for a crime then "I thought she was joking" is a defense against rape. (And note that there have been cases where the guy honestly believed he had consent--and it's worked as a defense.)