For comparison, see Augustus Taber Murray's translation (1924), which also mentions Ares:
 And they that held Argissa, and dwelt in Gyrtone, Orthe, and Elone, and the white city of Oloösson, these again had as leader Polypoetes, staunch in fight, son of Peirithous, whom immortal Zeus begat—even him whom glorious Hippodameia conceived to Peirithous on the day when he got him vengeance on the shaggy centaurs, and thrust them forth from Pelium, and drave them to the Aethices. Not alone was he, but with him was Leonteus, scion of Ares, the son of Caenus' son, Coronus, high of heart. And with them there followed forty black ships.
Not every translation mentions Ares in this context. For example, Theodore Alois Buckley's translation (1860) doesn't:
Those who possessed Argissa, and inhabited Gyrtone, and Orthe, and Elone, and the white city Oloosson: these the stout warrior Polypœtes, son of Pirithous, whom immortal Jove begat, commanded. Him renowned Hippodamia brought forth by Pirithous, on the day when he took vengeance on the shaggy Centaurs, and drove them from Mount Pelion, and chased them to the Æthiceans. He was not the only leader; with him commanded warlike Leonteus, son of magnanimous Coronus, the son of Cœneus. With these forty dark ships followed.
Going further back in time, Alexander Pope's translation (1715) does not mention Ares either:
Thy troops, Argissa, Polypœtes leads,
And Eleon, sheltered by Olympus' shades,
Gyrtonè's warriors; and where Orthè lies,
And Oloösson's chalky cliffs arise.
Sprung from Pirithoüs of immortal race,
The fruit of fair Hippodamè's embrace,
That day, when, hurled from Pelion's cloudy head,
To distant dens the shaggy Centaurs fled,
With Polypœtes joined in equal sway,
Leonteus leads, and forty ships obey.
Leonteus is the name of several characters in Greek mythology. The Leonteus in the Iliad is one of the commanders of the Lapiths. One of the kings of the Lapiths was Ixion, who may have been the son of Ares (or of a certain Leonteus according to Hyginus). Wikpedia lists one other Lapith who may have been a son of Ares (or of the Titan Iapetus) namely Dryas.
Neither Leonteus's father Coronus or his grandfather Caeneus are said to be descended from Ares.
The reference to Ares is consistent with Ares promise to fight on the side of the Greeks during the Trojan war. (At least that is what he did at the start; he later switched to the Trojan side.)