Classic stupidity isn’t fraud defense. It’s fairly effective, despite what this article is representing; if they prosecution can’t prove conspiracy or material fraud (smoking gun), they have an uphill battle proving their case.
Conservative attorney George Conway called Trump Jr.'s claims "ridiculous" because "Management representation letters are called management representation letters for a reason: They contain representations made 𝙗𝙮 𝙢𝙖𝙣𝙖𝙜𝙚𝙢𝙚𝙣𝙩 and it’s the 𝙖𝙘𝙘𝙤𝙪𝙣𝙩𝙖𝙣𝙩𝙨 who are entitled to rely upon them."
From the article, with their own emphasis.
Jr's version sounds a lot like "I didn't read the terms before I clicked Agree to install iTunes". Except the Terms for iTunes are the same for everyone and the documents he was signing her specifically made for him (in his position with the company).