If "Gentiles" refers to anyone "not a Jew", such as heathens or unsaved pagans.... why is the word capitalized as if it refers to a specific group?
The word is not capitalized in either the Hebrew (OT) or in the Greek (NT). Capitalization is not the issue. Context and meaning are the issue. An in-depth study of the use of the term "Gentiles" in both the OT and the NT makes plain that it cannot possibly mean the dispersed tribes of the northern kingdom. There are too many passages where such a meaning is clearly excluded. Do a search of the word, look up the passages, and you will see.