I wonder whether the box was like a product that you can buy in that world. Or if it was like... a regular box that got enchanted to hide the books. For the latter, maybe he asked one of his friend to do the enchantment?
It will interesting to see what will happened once it's gets to the point when the MC is strong enough to breeze through the upper floors. (If the manga or the LN lasted that long.)
In the first chapter, the fruit has description of "A fruit with tough skin but delicious." Although I don't think it should peeled the way it was drawn in this chapter, based on the previous description. So I guess it's either, artist just draw regular orange, or the MC had grown much...