Lindt is pretty good as packaged chocolate goes. You can always find some fancy artisanal chocolatier if you can afford to spend a few bucks per chocolate but for a HS student Lindt is pretty high tier.
Premium, I definitely agree. But luxury is pushing it imo, given the prices and ingredients used. Imo luxury chocolate is either artisanal and/or has extremely high quality standards (e.g having as little stuff that is not pure cocoa and sugar as possible in its ingredients), and thus even more expensive than Lindt.
As I already said in another comment, this is a eurocentric point of view. When I lived in Canada I didn't buy Lindt because they were almost twice as expensive as what I was used to.
Lindt is positioned as a premium supermarket brand in some places where it is usually a little better and more expensive than the default brand eg Cadbury. For many people it would be seen as a bit of a treat over their regular supermarket brand. Some markets have more appreciation and better access to good chocolate than others but it is a relative thing.