Scully’s interpretation of this passage is that Philoktetes and Odysseus are offering competing interpretations of some kind of omen, and Scully gives us a “burst of light” and “distant rumbling” as a plausible candidate for an omen that might support these interpretations. So the uncertainty over exactly what it might represent is deliberate.
Philoktetes interprets the omen as the “shooting flame worked up by Hephestos”, meaning an eruption of the volcano Mosychlus on Lemnos, which was sacred to Hephaestus, the god of blacksmiths and metal-workers, and said to have been the location of his forge. In the Iliad, Hephaestus reminds his mother Hera that when Zeus hurled him out of Olympus he had landed on Lemnos:
“Be patient, my mother, and endure for all your grief, lest, dear as you are to me, my eyes see you stricken, and then I shall in no way be able to succour you for all my sorrow; for a hard foe is the Olympian to meet in strife. On a time before this, when I was striving to save you, he caught me by the foot and hurled me from the heavenly threshold; the whole day long I was carried headlong, and at sunset I fell in Lemnos, and but little life was in me. There the Sintian folk quickly tended me for my fall.”
Homer. The Iliad, I.585–593. Translated by Samuel Butler (1924). London: Heinemann.
The volcano has already been referred to in the play, when Philoktetes called on Neoptolemus to cast him into it to end his sufferings:
Philoktetes O son, noble youth, seize me, burn me up, true friend, in that fire famed as Lemnian.
Sophocles. Philoktetes, lines 799–800. Translated by Richard C. Jebb (1898). Cambridge University Press.
Jebb adds a note on these lines:
The volcanic mountain called Μόσυχλοσς appears to have been on the east coast of Lemnos, south of the rocky promontory to which the cave of Philoctetes was adjacent. No volcanic crater can now be traced in Lemnos; and it is probable that the ancient Mosychlus has been submerged.
Richard C. Jebb (1885). Philoctetes, p. 130. Cambridge University Press.
By constrast, Odysseus interprets the omen as a bolt of lightning hurled by Zeus. Odysseus says that he “carries out his [Zeus’s] orders” because it was Zeus who ordained that Philoktetes must be taken to Troy to be healed and win the war for the Achaeans. Probably this was a familiar part of the myth as far as Sophocles and his audience were concerned, but it must come as a surprise to Philoktetes, who has only been told only that Helenus has so prophesied:
Neoptolemus How I know these things are so ordained, I will tell you. We have a Trojan prisoner, Helenus, foremost among seers, who says plainly that all this must come to pass, and further, that this very summer must see the complete capture of Troy. Otherwise he willingly gives himself over for execution, if these prophecies of his prove false.
Sophocles. Philoktetes, lines 1336–1342. Translated by Richard C. Jebb (1898). Cambridge University Press.
The role of Zeus is confirmed, however, by Herakles when he appears at the end of the play:
Herakles For your sake I have left my divine seat and come to reveal to you the purposes of Zeus, and to halt the journey on which you are departing. Hearken to my words.
Sophocles. Philoktetes, lines 1413–1417. Translated by Richard C. Jebb (1898). Cambridge University Press.
This idea, that Philoktetes and Odysseus are offering competing explanations of an omen, is quite ingenious. Jebb says that, in respect of Philoktetes’ line at least, this idea goes back to a scholium (a marginal comment in a manuscript), but adds:
We need not suppose, with the schol[iast],† that the epithet‡ refers directly to Hephaestus working at his forge within the mountain. […] Philoctetes has appealed to the local deities of Lemnos. Odysseus retorts that Zeus is above them all, and that Zeus (by his oracle) has given the behest which is now being executed.
Richard C. Jebb (1885). Philoctetes, p. 159. Cambridge University Press.
† See Richard Brunck (1810), Scholia Graeca in Sophoclem, p. 322 for the scholium. ‡ Ἡφαιστότευκτον (Hephaistoteukton) meaning “wrought by Hephaestus”.