According to Media Matters:
Many media figures who have reported Sen. George Allen's claim not to know what the term "macaca" means have omitted the fact that Allen's mother grew up in North Africa.Many reports by mainstream media, including this Washington Post story, neglected to share this information about Allen's mother. Although it doesn't provide absolute proof that Allen knew he was using a slur when he called the Webb staffer a "macaca," this detail certainly casts significant doubt on Allen's claim: "I don't know what [the word] means."
However, on the August 16 edition of MSNBC's Hardball, Chris Matthews acknowledged the role her background may have played in Allen's use of the word, which, as a racial slur, reportedly originated in North Africa.
Prompted by The New Republic's Ryan Lizza during the August 16 edition of MSNBC's Hardball, host Chris Matthews suggested that Senator George F. Allen's (R-VA) mother's ties to the North African nation of Tunisia might explain how Allen came to use the derogatory term "macaca" to describe one of his opponent's campaign volunteers.
... while the word's use as a slur originates in North Africa, many media figures who reported Allen's claim not to know what the term means ... (and) left out the fact that Allen's mother grew up in Tunisia ..."