You will notice that all the other asteroid-moons in Sol system in FE2 are also omitted from the ED system map: Amalthea around Jupiter, Hyperion around Saturn, Miranda around Uranus and Nereid around Neptune. FE2's stellar forge could procedurally create such "asteroidal moons", but never created similarly-sized "asteroidal planets" or "free asteroids". They decided in ED simply to not create asteroid-sized moons at all.
The omission of Ceres is, perhaps a bigger "blunder". Back in the Great Planet Nomenclature War, the pro-Pluto faction generally agreed that, if Pluto were to be defined as a planet, then in fairness Ceres ought to be reclassified as a planet too (Ceres was originally classified a planet way back when it was discovered, but lost that status a few years later once the other large asteroids were also found). Ceres apparently died in ED when the "no asteroids in ED" policy came about.
When they added Quaoar, Persephone and the other trans-Pluto planets to Sol system, they couldn't add Ceres easily at the same time. Tacking new planets on to the end of a star system is "easy" compared to trying to insert a new planet in between two other planets. That's because each star, planet and moon has a number, and adding a new Planet 7 to Sol system would have meant re-editing all the other planets from 8 outwards.
Analysing the journal files shows that Sol system does in fact have a "missing planet" according to ED's calculations: Planet 20, in between Saturn and Uranus. Since there's no significant objects orbiting out in that region, and since Halley's Comet has a semi-major axis that lies exactly in that gap where Planet 20 ought to be, it is generally assumed that Halley's Comet is that "missing planet", a "currently invisible comet" present in Sol System. But there is no such gap in the numbering between Mars and Jupiter.