There was a theory that he was intentionally TRYING to lose the election, that the whole thing was a publicity stunt for his (canceled due to him becoming President) then not-quite-upcoming "Trump TV" venture (Which was basically Fox News starring Trump)
He looks genuinely surprised and upset that he won in the pics showing his reaction, and so did Ivanka.
I can totally buy that his plan was to win the primary, lose the general, and sell not him as a president, but the fantasy of the White Utopia he'd create if he was President... and the conspiracy theories that Hilary won by cheating...
But then he fucked up when the plan went horribly right and he became the President for realsies.