That's an illegal dribble in a HS game.
I had to watch it several times using the pause button to get this analysis.
The following analyzes the action under NFHS rules. I have no idea about the NBA ruling, nor do I care. I am not saying that the NBA officials were incorrect. I am simply not commenting on that at all.
1:17 on the video: The player ends his dribble by grasping the ball with two hands at the top of the FT semicircle. At this time his LEFT FOOT is on the floor and his right foot is in the air. So his LEFT FOOT will be his pivot when the other foot touches. The right foot comes down just inside the FT line as the player has let go of the ball with his left hand and is pushing it upward with his right hand. The ball is released into the air and his left foot comes off the floor while the right foot is still in contact with the floor. This constitutes the player lifting his pivot foot. If he puts it back down, he must have either passed, shot, or dribbled before then. So if he were able to jump off his right foot at this moment without having his left foot touch the floor, then he could legally rise into the air, grab the ball, and dunk it. However, the player now steps with his left foot, touching the court between the dotted half of the FT circle and restricted area semicircle around the basket, and proceeds to jump off that foot by swinging his right foot forward (This foot does not touch the floor at this point), rise into the air, catch the ball, and dunk it. Under NFHS rules as soon as he touched the ball in the air after stepping with his pivot foot, he committed an illegal dribble violation (or a travel according to a silly new revision of a long standing case book play).
More garbage from the NFHS