In that case Weston's comment about institutional racism would seem to be accurate, and as such, surely, they are open to discrimination law suits. I would hope that, by now, Universities operated a "colour blind"' approach to making offers, much as is supposed to happen with employment law, and that therefore, as you have mentioned, other factors must be in play.
However it falls, 'positive' assistance towards a particular group is implicitly discriminatory against, and is a disincentive for, others.