This article claims that one opinion is that the word "Ivri" is related to "Ever", one of Noah's descendants.
The Bible uses the term "Ivri" in many places. Avram was called an "Ivri" (Breishit (Gen.) 14:13). Considering that Ever had many non-Jewish (i.e. non-Abraham) desendants, or for that matter, descendants of Ishma'el or Esav, etc. why aren't these descendants also called "Ivrim" or "Hebrews" based on this definition?