Ethnocentrism is the practice of assessing foreign cultures through the lens of the native; such an individual feels aghast and furious in case anything he or she observes differs from his or her usual environment. In fact, ethnocentric people use their own cultures as the universal measurement of what is appropriate and what is not, considering them the only rational, reasonable worldviews. It may be difficult to look outside those frameworks, primarily because many do not even realize the need to do that.
Miner, meanwhile, seeks to help his readers distance themselves from the American culture of the middle of the twentieth century and regard it independently. The fictive little-known indigenous tribe is simply the covering under which the author satirizes the contemporary phenomena in the society of the United States, such as the way the healthcare system treats the population.
A hint at this is present in the description of the latipso guardians, who do not let the patients in and then out unless they are able to give rich gifts. This doubtlessly is the point at which the author expects the readers to notice the similarities between the culture he is describing and their own. Such an approach allows for an outside perspective on the disadvantages of the native environment, which are not necessarily apparent from within it.