It’s not an oxymoron, the idea is that when there are forces with opposed interests, one has to win. Note that this is talking about opposed interests, not interests that are merely in conflict.

So no matter how much you try to make concessions for the other, you have to choose if you want a bourgeois dictatorship (liberal democracy) or a proletariat dictatorship (people’s democracy) at the end of the day. Socialists just use less euphemism, and therefore accused of “admitting to dictatorship”, but a liberal democracy is the exact same type of dictatorship. The bourgeoisie interests dictate, and they make concessions for the sake of the proletariat.