But luxury is superfluous; perhaps even by definition.

Why lack of superfluous boxes is good when the product itself is superfluous?

The product isn’t superfluous. He needed a watch. The superfluous part was the craftsmanship that went into the watch vs buying a cheap mass produced piece.

Hence why I said it’s a property of the piece itself.

Then why choose a product with superfluous craftsmanship and praise the lack of superfluous boxes?

I can only assume he’s praising it because he cannot wear the boxes. But I’m not the author so you’ll have to ask him that question.