There's two very different and hard to reconcile arguments to be had in a casting issue like this. First, the tendency for white people to view casting as a white/non-white issue. The idea that whiteness is the norm and all other races and ethnicities are a deviation and thus all belong in the same category is hugely problematic, both within niches like this and one a broader scale. The oppression, stereotypes, and historical subjugation that different races have faced, both in American society and around the world, are vastly different, and to boil them all down to an amalgamation is a disservice to those groups' unique perspectives and histories, and a form of racism in itself.
But, at the same time, in a production that necessitates (or, regardless of previous casting, should necessitate) a POC, I would certainly feel more comfortable with an actress of color of any race being offered the role than I would a white actress. While an Asian or a black actress may not carry the same historical/ancestral/contemporary context a Romani woman would, she would at the very least understand what it means to be a WOC. And, beyond any sort of potential racial undertones within the text of the show itself, she would be given the opportunity to lead a musical, an opportunity that (especially in high school theatre) very few get the opportunity to. That's all relevant if the production must be Hunchback, though. The second major issue with this controversy is that the director did not know his talent pool, or did and chose to ignore it.
A more extreme example of this was an all-white HS Hairspray a few years back in Texas, a little after my own Texas HS put it on. Knowing good and well that the demographics of the school could not support a show that required racial diversity, the director decided to move forward and cast from their talent pool, which was white. If you, at any level of theatre, want to do a production and do not have the required cast for it, you cannot do it. Plain and simple. I particularly liked Rainah's post on the matter. When my school did Hairspray, our usual crowd of actors was predominately white and Hispanic. Before the show was announced, my director worked with the choir director and other campus leaders to get the word out that the show was going to require black actors. Only when he felt that we had a strong casting pool outside of the usual faces did he announce auditions. And, when those black actors who had previously been uninterested in theatre (some of whom because they saw our previous shows and didn't see a place for themselves) were cast, they were supported. They were given vocal lessons and dance lessons and just genuinely emotionally encouraged, and many of those actors came back season after season. In just one production, our department went from predominately white to very evenly represented, and that diversity has maintained years down the line. That is why casting like this, especially in a high school or community setting, is so important. To some, it may seem like no big deal, but to those who so rarely see themselves on stage, roles designed for POC can be truly transformative on a personal and structural level.