"When he saw a fire," meaning: in his own estimation (and it was, in fact, a light). "He said to his family, 'Stay here; indeed, I have perceived a fire,'" meaning: I have seen it. "'Perhaps I can bring you a brand from it or find at the fire some guidance,'" meaning: guides who will direct him to the road.
Muhammad said: A qabas (brand) is what you take on the end of a stick from the fire, or on the end of a wick.