Read or re-read the article. The proms are NOT sponsored by the school but by the parents away from the school as you are suggesting. The kids themselves seem to want to have one integrated prom, and that’s great. Hope it works.
Myself, I always thought proms were a huge waste of time in high school. I detested them. The JROTC military balls had more prestige, but many high schools dropped JROTC long ago.