Individuals that are interested in what interests others might have are not subordinating anything, it is what interests them. IOW, it happens to be one of their many interests; that makes it a self interest. There is no glaring contradiction. There is only a denial by Rand's detractors, that an individual could possibly be interested in someone else's interests. The fact is that Rand herself was interested in the welfare of others. That's why she held and defended the noninitiation of force principle as central to her moral code.
It's not altruism if it "interests" them. Quite a non sequitur.