Technically, he doesn't talk there about liberals, but about "egalitarians." And he says in the preface that that article is directed towards "socialism": the essay "locates the prime horror of socialism as

the egalitarian attempt to stamp out diversity among individuals and groups." He also says, "If individual diversity were not the universal rule, then the argument for liberty would be weak indeed. For if individuals were as

interchangeable as ants, why should anyone worry about maximizing the opportunity for every person to develop his mind and his faculties and his personality to the fullest extent possible?"

So he's really talking about those who want to maximize equality of outcomes. The problem is that anything that conflicts with anarcho-capitalism can be strawmanned as seeking that "socialist" end. That's what the GOP is doing with Harris's policy of combatting price gouging: it's "communism," they say. Anyway, egalitarianism isn't just a communist value but a liberal humanistic one, so Rothbard's article is vague.