Oneness and Buddhism are sometimes mixed together. As with most claims, it is unclear what this means. And this lack of clarity results in delusion and mistaken views.
Oneness is usually made out to be homogenizing. An experience of oneness, on this view, would be a dropping away of difference and an arising of sameness. Rhetorically, this view of oneness is used to erase difference, as in your different experience of this predominantly white sangha is superficial because really we are all one. Metaphysically, this view raises questions about monism: are we all just one thing or are we all made up of the same kind of thing?
More to the point, this is a particular view of oneness and it isn’t the only view and, from the standpoint of Buddhism as a practice of liberation, it is unhelpful.
Another view of oneness that I believe is helpful on the path toward liberation is oneness as utter particularity, as the absolute uniqueness and non-sameness of each and every particular thing.
Experientially, oneness as utter particularity would be an experience that fully embodies, embraces, and realizes the unique, heterogenous, and not-similar-to-anything-else moment of experiential arising. Rhetorically, this view of oneness would embrace difference, as in your different experience of this sangha is something we must pay attention to because our experience of it as homogenous is rooted in ignorance. Metaphysically, this view points in the direction of deep particularity and causality, in other words, in the direction of karma and responsibility.
Furthermore, oneness as utter particularity embraces and radicalizes oneness as homogeneity, whereas oneness as homogeneity erases particularity. Each of us, each moment of arising of experiential awareness, is utterly particular. In that sense, there is a sameness in each moment of arising, in each thing. It is the sameness that can only be found in complete difference.
Realizing this sameness in complete and utter difference is the path of liberation.