Earlier in the scene, the Captain described for King Duncan the bravery and courage of Macbeth (and Banquo) on the battlefield: how, first, Macbeth fought against the traitor Macdonwald, brutally killing and beheading him, and, then, how Macbeth turned to face the Norwegian king's forces next. After this, Duncan sends the Captain for medical help.
When the Captain leaves, the Thanes of Ross and Angus enter, having come from Fife, and Ross describes the conflict between "Bellona's bridegroom" and the Thane of Cawdor, another traitor, fighting on the side of Norway. We don't know precisely where the Captain came from, where he saw Macbeth fighting, but it doesn't seem to be the same location from which Ross has come. Ross says that, in Fife, "the Norweyan banners flout the sky," and the Captain provided no such description of the location from which he came (1.2.49).
Further, Ross never uses Macbeth's name specifically, and so it seems less and less likely that the reference to Mars, the god of war, (and Bellona's husband) is being applied to Macbeth. Because Ross has already named Fife, it seems more likely that this allusion refers to Macduff, the Thane of Fife, who we later discover to be a formidable warrior himself when he bests and beheads Macbeth in combat. We cannot, however, be totally sure.