BBall -- Congrats to your son! He looks great on the video. To my eyes, his pitch looks more like a CB than a Slider. Obviously, it is difficult to tell from the film.
Typically, I'm used to a Slider being a tighter break, with velocity closer to the FB (-3 to -5). The typical indicator of a good Slider is a tight spin with a "dot" the hitter sees. The CB grip/release (the Karate chop grip) typically flies with with a top spin rotation coming to the hitter.
I guess it matters less what he calls it (he could call it Fred), than that he can throw it for strikes, and that he is not straining his arm, or torquing it during the delivery to achieve the rotation. Best wishes to him for a successful year and career.