Science is not just about formulas and theory's, in essence its about the gathering of facts that we both know to be true and can prove to be true.
Anthropology is an older form of science, while many fields of study have changed dramatically over the years. Anthropology remains largely the same now as when it was created. Its all about learning about humans, how we evolved and how we have developed culturally, socially etc..
Its a difficult thing to explain, have a look at the site below and come to your own conclusion:
Anthropology is the study of humans. Science is the collection and study of the structure of the natural world by the use of observation. Many pillars of anthropology are quite scientific such as the studies of Familial ties, Subsistence structures, and archaeology. However much of anthropology is also a subjective opinion. One example of this subjectiveness is the debate on whether race exists. This debate is Quite heated among anthropologists. The "correct" answer to this debate would be the one that is true even without human interference. Most people cant agree with what race is or what it is not. Because this debate is so dominated by opinion and what each person thinks it is not science. Just in the same way political candidates are not a scientist even though there is a "Political science" field.
But tends to more of an art/literature. That's because it represents literary pieces of art, which help us understand other people of our kind, mankind. Scientific formulas apply to all time, I mean they're linear (A causes B). However, anthropological studying results constantly change. There is no rule or formula that is surely applies to all cultures. Plus, anthropology includes creative activity, the art of observing and interacting and understanding other cultures. Therefore, I believe anthropology is a literary art.