On the one hand, Chappa's gains must be manyfold for him to think he has a chance.
I mean, he can't think that Goku hasn't improved much since 22nd TB; just growing
into adulthood is an obvious great power boost for Goku, add the training to that and
Chappa definitely expected a much stronger Goku than the one he had fought.
On the other hand, Chappa seemed past his prime, so he logically can't have great gains.
Is it possible he was so cocky that he just believed he would win this time because shut
up?