I did question Belias' appearance in that quest, as he was a fire elemental esper in FFXII and we already have a fire elemental primal with Ifrit. Then again,
The Ascians were the ones who let him summon Belias. Belias is one of the espers from FFXII. We know the Ascians worship Zodiark. It's possible that Ivalice's roster of espers will be the "dark" counterparts of Eorzea's primals (e.g. Belias for Ifrit, Chaos for Garuda, Mateus for Shiva, Adrammelech for Ramuh, Hashmal for Titan, Zodiark for Hydaelyn, etc.)