I don't know about any one specific concert, but, while hip-hop's market share has certainly increased over the years, and has likely become more popular in the last 15 years than ever before, it has been popular among white audiences in major cities since at least the mid-80s. Yes, NWA scared a large portion of the white establishment, but many white Gen X-ers were already rejecting the same establishment that itself was gagging on Straight Outta Compton, and either empathized with the politics of the record or were able to see past them for the sake of enjoying the tracks. I have not seen the film, but unless the crowd was mostly white, The portrayal was likely accurate.