A very touching moment

not to mention you have to empty your lungs of air to be able to sink and stay down like that

He tried but he messed it up a little

He really didn't try, though. He jumped in, realized his form was a bit off and immediately sank to the bottom in defeat. Talk about giving up.

Gonna repeat this again, he is a diver. He is graded from the moment he leaves the board, to slightly after he he dives into the water. THIS IN NO WAY MEANS HE STOPPED TRYING AT ANY POINT WHILE BEING GRADED. I'm sure he still gave it his all the entire time. BUT, after entering the water, he already knew he wasn't "perfect" in his execution, which in diving you pretty much HAVE to be to win. He already crossed the proverbial finish line so there's no "giving up" or "quitting" but long before all the announcers and the crowd realize that he isn't gonna win, HE knew he was no longer going to win. It was just a moment of deep disappointment for himself.
Another example away from sports would be taking an exam in school. Say you do the entire exam and work your ass off on it, studying for hours and working hard the entire time you are taking it, then turn it in and leave and 5 minutes later realize you screwed up big at the start of a problem, which in turn screwed up the next 10 answers

Long before your teacher or any of your classmates know it, YOU know that you screwed up your score and will definitely not make the top grade in the class. Doesn't mean you are somehow a quitter.