How is the new south park episode making fun of high school musical 3?

I have never seen any of these movies. Is the guy who keeps slapping people someone from the movie and what does slapping people have to do with him? Who is the girl with the pig nose that they show while they watch the movie? Is the girl that they show walking with the black person in the cafateria the girl that had the nude pictures online? And who is brydan in the movie?How is the new south park episode making fun of high school musical 3?
My daughter watches the movies all of the time. I didn't get to catch the first part of the show, but here is what I cought.





Brydon is supposed to be Zack Effron, but he secretly likes sports and is supposed to dance, the opposite of the movie.





His dad in Southpark is supposed to be the opposite of his dad in the movie. In the movie his dad didn't want him to sing. How is the new south park episode making fun of high school musical 3?
I haven't seen the movies either but if you listen closely they are singing about the status quo which would account for the one black guy and one fat girl in the scene. I can't help you with the other two.