After hearing Luke's words, Ariel gave it some thought.
Certainly, the probability that he's forgotten is high.
The time when Rudeus and Sylphy separated was eight years ago.
If there's eight years, then people can start to forget about people.
At the very least, it seems this past year, Sylphy hadn't heard the words "Sylphy" from Rudeus's mouth.
If that's the case, then the probability that he'd forgotten the very existence of the one known as Sylphiette is high.