The OP left the context out. The elf thinking that was comparing what he heard of alienage from Ferelden (small closed off areas) to the large elven slum in Halamshiral and deciding that the High Quarters sounded like an alienage because it was a small closed off area.
It's normal that the former land of the elves has more elf in then humans, there have been no reason to displace them. Even for cheap labor. The passage leaves no doubt that Orlesians nobles are in control of the area, it's just that most of the peasants are elven and not humans.
Though there does seem to have been a large scale displacement, because that's the origin of the Alienages.
Codex: The City Elves (Non-elf version)
When the holy Exalted March of the Dales resulted in the dissolution of the elven kingdom, leaving a great many elves homeless once again, the Divine Renata I declared that all lands loyal to the Chantry must give the elves refuge within their own walls. Considering the atrocities committed by the elves at Red Crossing, this was a great testament to the Chantry's charity. There was one condition, however--the elves were to lay aside their pagan gods and live under the rule of the Chantry.
Some of the elves refused our goodwill. They banded together to form the wandering Dalish elves, keeping their old elven ways--and their hatred of humans--alive. To this day, Dalish elves still terrorize those of us who stray too close to their camps. Most of the elves, however, saw that it was wisest to live under the protection of humans.
And so we took the elves into our cities and tried to integrate them. We invited them into our own homes and gave them jobs as servants and farmhands. Here, in Denerim, the elves even have their own quarter, governed by an elven keeper. Most have proven to be productive members of society. Still, a small segment of the elven community remains dissatisfied. These troublemakers and malcontents roam the streets causing mayhem, rebelling against authority and making a general nuisance of themselves.
--From Ferelden: Folklore and History, by Sister Petrine, Chantry scholar
Which is why I was previously under the impression that there wasn't a large elven population in the Dales.