When is a good person a Samaritan?

Today's Boston Globe has a short story headlined "Good Samaritan, 30, dies of stab wounds." I was intrigued since, like most people, I often wonder whether I have enough compassion to help out a stranger in need. But the story is weirdly vague about how the people involved -- the "Samaritan" named Scott Gilbeau, the woman in distress who is not identified, and the attacker with the memorable name of Roy B. Bash -- came to know each other.

Gilbeau, Bash, and two women had been at a bar in Vergennes before returning to the Hinesburg trailer where Bash and his girlfriend lived. The couples had retired to separate rooms for the night when Gilbeau heard Bash and his girlfriend fighting, according to the affidavit filed by Vermont State Police Detective Sergeant James Whitcomb.

Gilbeau was undoubtedly heroic, but I thought a Good Samaritan, by definition, was someone who goes out of his way (or misses church, in the original story) to help a stranger. Here the term just seems confusing, and even euphemistic in a way I can't figure out. Why not just say that the two men were friends or neighbors, or some other vague term that doesn't come from a parable specifically about providing aid to someone one has never met before?