Not sure about the upper class bit ... for the white vote it seems pretty clear that it was the rural lower-middle class voters that voted no.

Strange thing about this referendum is that wealthy traditional liberal party voters and indigenous people have probably never been more united in a poll.

I've anecdotal talk that a lot of rural people were worried about having their land taken. Dog whistling FUD amongst those with something to lose or to feel bitter about seems to be what killed this ... not plain privilege amongst the upper-middle classes I'd say. The wealthy that killed this are probably the super wealthy who manipulated things behind the scenes.