▲由于历史的原因，名词 Indian 有两个不同的意思：

1. a native or national of India, or a person of Indian descent 印度人；印度后裔

2. an American Indian 印第安人

印第安人是美洲原住民，是除爱斯基摩人外的所有美洲土著居民的总称。美洲土著居民中的绝大多数均为印第安人，分布于南北美洲各国，传统将其划归蒙古人种美洲支系。印地安人属于黄种人，哥伦布航海发现美洲时，误以是印度，就将土著居民称作 Indians，之后因习惯未予更正，为区别一般称印地安人为“西”印度人，真正的印度人为“东”印度人。（来自网络）

▲《新牛津英语大词典》有这样一段说明，对于你的问题的理解会有所帮助：

The native peoples ofAmericacame to be described as Indian as a result of Christopher Columbus and other voyagers in the 15th–16th centuries believing that, when they reached the east coast of America, they had reached part of Indiaby a new route. The terms Indian and Red Indian are today regarded as old-fashioned and inappropriate, recalling, as they do, the stereotypical portraits of the Wild West. American Indian, however, is well established, although the preference where possible is to make reference to specific peoples, as Apache, Delaware, and so on.