The immediate source of this entry is unknown, but compare Malalas p.19.1ff Dindorf and [John of Antioch] fr.61.1 FHG (4.542) = 6.1b Roberto; cf. generally eta 235, eta 661.
[1] For Ninus see nu 417. Neither Ninus nor any name like Thourras appear in the Assyrian king-lists (web address 1 below). From Roman times on, Ninus is the eponymous hero of Nineveh but Thourras is much later. [In Joel p.4 Bekker, from the thirteenth century, it is 'Thurras'.] The name Thourras seems to have derived from a misunderstanding of thouros, an epithet of Ares in Homer, Iliad 15.127 (etc.), "violent Ares," which strayed into the muddled Greek and Roman notion of Near Eastern history.
[2] Mars.
[3] The descendants of Noah's son Japheth are listed in Genesis 10:2-5, and the lexicographer must have identified one of them (probably Magog) with the Caucasus.
[4] What the lexicographer has in mind is "Bel and the Dragon." It appears in the Apocrypha as the 14th chapter of Daniel and describes the undoing of the priests of Bel but does not call him the god of war. Bel and Baal are here identified and are, in fact, cognate names; cf. beta 1 and beta 24.