All-women spaces exist to provide safe harbour from harassing men, because that's all said organisation can realistically do to ensure it doesn't happen.
School environments are very different in that they are much more controlled and that educators can take on a more disciplinary role.
If the non-white kids are getting harassment from the white kids to the point where such a safe space is necessary, normally I wouldn't be able to tell if that's a bigger condemnation of the school's inability to handle racism or the community's tolerance for racism in their kids.
The fact that there's a fucking bomb threat over this however, is very enlightening of the community in which this school operates. It really reveals just how hostile an environment that community really is to minorities.
So with that in mind I can definitely see the rationale for a PoC-only playdate.