You might not like that the world works that way, but as a business it's wise to not deny reality.
_That_ person is the problem in the office, not the person who bought sweets online and probably shared them with some of the office.
If anything, the packaging helped reveal an oddball at the office.
Wait, what? In fashion, sure, by definition - but when I'm choosing between Persil and Tide, or Coke and Pepsi, or Pizza Hut and Domino's, I'm primarily looking at how good it is at whatever I want it to do. Which one cleans better, which one tastes better?
There's a certain point where many people start buying things more as social signalling than as actual useful things, but I'd disagree that the vast majority of brands could be fashion items in this way. The rest use their brands to evoke trustworthiness - "I know that this will do what I want".
That said, that does not explain people reading the kinds of graphic novels and magazines they do in plain sight in public on trains in parks, etc.
Trains and parks, by contrast, are generally considered an appropriate context to consume these kinds of materials. That being said, book covers are also far more commonly used for exactly the same reasons.