According to the website "Appetite vs. hunger", the difference is very similar to what you were saying:
> Hunger is the need to eat.
Hunger is instinctive, it is the body's way of letting you know it needs sustenance.
and
> Appetite is the desire to eat.
It is a coordination between the brain and the stomach, this is learned behaviour.
Some further information can be found in the article preview "The Biological Nature of Appetite" (Stellar, 1992)