I couldn't prove the author of the book of Hebrews would not call fellow Jews Hebrews, but in Genesis alone Abram was called one, so was Joseph by the Egyptians. It was not an offensive word to Jews.
Genesis 14:13 (KJV)
[SUP]13 [/SUP] And there came one that had escaped, and told Abram the Hebrew; for he dwelt in the plain of Mamre the Amorite, brother of Eshcol, and brother of Aner: and these were confederate with Abram.
[HR][/HR] Genesis 39:14 (KJV)
[SUP]14 [/SUP] That she called unto the men of her house, and spake unto them, saying, See, he hath brought in an Hebrew unto us to mock us; he came in unto me to lie with me, and I cried with a loud voice:
The Bible uses "Hebrew" 26 times, and the native language of the Jews is "the Hebrew tongue". Whehter a Jew of Judah, or a Hebrew of one of the other tribes of Israel, all were Hebrews to each other.
BTW, the author could be none other than Paul, who mastered Judaism enough to explain it in Christian terms, and explain Christianity in Judaism terms, not that Christianity is based on the other. Ours is a NEW covenant in Christ.