How old was the cashier? Just curious, because it is still pretty silly the way that was handled. I could see the cashier thinking the box gets refilled for more packs, but then she goes and just charges you $2. for the whole box and reinforces her stupidity. Maybe this little episode rattled her and her brain turned off. I've seen this happen with people before. They get into a social situation that they are not used to and their brain shuts down. Funny but also sad.
I kind of thought it was two different cashiers, one who was giving away packs, and one who was worried about the empty box.
I've had cashier problems when offering loose change to even out a sale, and once when trying to use a dollar coin in a Walmart. One time I got to the register at Walmart, and the clerk was scrutinizing change in his drawer because he thought it was counterfeit. They were older silver quarters, I could tell from the clinking sounds, and I wound up getting them as change - he was happy, and I was happy.