What's his incentive for lying? I totally understand being a skeptical that a relatively low level contractor got access to everything, but I don't understand

What's his incentive for lying? I totally understand being a skeptical that a relatively low level contractor got access to everything, but I don't understand what would motivate someone to go public and incite the wrath of us intelligence if he didn't at least believe he was telling the truth. If he's a Chinese mole, or in cahoots with enemies of the state, it doesn't seem like leaking some slides to the guardian and then filming a confession would be the way to go about it. Is the argument just that he's incompetent/confused, or am I missing something? Genuine question.