Many commentators make this assumption because Ayn Rand advocated self-interest, and titled her anthology on ethics "The Virtue of Selfishness." But in doing so they are making two assumptions: that "morality," by definition, refers to altruism and self-sacrifice; and that unprincipled, emotionalist action is in fact in one's self-interest. Ayn Rand rejected both of these premises.
Morality is "code of values to guide man’s choices and actions." There is no reason to assume a code of values is necessarily altruistic or self-sacrificial. As I've mentioned before, far from eschewing morality, one of Ayn Rand's major criticisms of altruism is that it substitutes a beneficiary (others) for a code of actual values to pursue and virtues to embody. Another of her major criticisms of altruism was that, given the only way to fully embody self-sacrifice is not to live at all, altruism gives man an unemployable moral code, leaving one without a moral code at all.
What Ayn Rand promoted was not renouncing ethics but an alternative conception of ethics, which can be summarized as "rational self-interest."
My morality, the morality of reason, is contained in a single axiom: existence exists—and in a single choice: to live. The rest proceeds from these. To live, man must hold three things as the supreme and ruling values of his life: Reason—Purpose—Self-esteem. Reason, as his only tool of knowledge—Purpose, as his choice of the happiness which that tool must proceed to achieve—Self-esteem, as his inviolate certainty that his mind is competent to think and his person is worthy of happiness, which means: is worthy of living. These three values imply and require all of man’s virtues, and all his virtues pertain to the relation of existence and consciousness: rationality, independence, integrity, honesty, justice, productiveness, pride.This also addresses the other side of this myth: that Ayn Rand advocated arbitrary, emotionalist behavior, or using "whatever feels good" as a standard of value, i.e. hedonism. In reality, Ayn Rand did advance a standard of morality and, further (as indicated in the previous quote) that rationality is the primary virtue.
This is the fallacy inherent in hedonism—in any variant of ethical hedonism, personal or social, individual or collective. “Happiness” can properly be the purpose of ethics, but not the standard. The task of ethics is to define man’s proper code of values and thus to give him the means of achieving happiness. To declare, as the ethical hedonists do, that “the proper value is whatever gives you pleasure” is to declare that “the proper value is whatever you happen to value”—which is an act of intellectual and philosophical abdication, an act which merely proclaims the futility of ethics and invites all men to play it deuces wild.Ayn Rand condemned hedonism as well as what she called whim-worship, and argued that emotions are "are produced by man’s premises," so they cannot be primary to them, and should not be treated as though they are.
The broader take away from this post should be that Ayn Rand was a philosopher that re-framed issues like morality. Rand did not merely take positions from the terms made available by today's cultural philosophy, but questioned the basic ideas underlying our cultural philosophy, ideas that most people adapt from the culture they live in and assume without evaluating or even acknowledging them. Her ideas need to be studied appropriately, or else you will project on to her ideas she not only rejected, but spent her career criticizing. And if, worse, you learn about her ideas from the paraphrases of others who have done such projecting, you will know less about them than you had before.