I don't see the point in making this kind of statement. You're dealing in the absurd since you don't know what tomorrow will bring. It's more arrogance than it is confidence. A humble person realizes that you don't control every factor in this world. You work hard and hopefully you receive the fruits of your labor.
Saying you're going to win prior to having the match is arrogant and shows a lack of respect for the opponent.
The only thing important here to me is who is saying this and not what was said. I agree with your premise (and others) of showing it on the field and to show respect for the opponent. I also agree that you can have high goals without advertising it.
The source is what is intriguing here. As far as I can tell this is something out of character for Kalil and it comes on the heels of a major transaction involving a first round draft pick in the unit he is the leader of. I give him a pass. The guy sounds genuinely excited to me and most likely regrets having said it already.