Kiwi maths

Look at this picture, which was taken at the Auckland Lantern Festival last night. Notice anything interesting? (Besides the spelling of Mongolia) My wife was quite amused by it, while we were waiting in the long queue for the lamb kebabs, because it's another example of a phenomenon that she'd often seen in New Zealand and a contrast to what you'd see in China. In China, you'd often see signs like this but only when there is a discount for buying more. $2.5/p = $10/4p is simple maths, so it makes you think of numerous possibilities: (1) their maths is bad and they don't realise that it is not a discount; (2) they think your maths is bad and you won't realise that $10/4p and buy more for no discount; (3) they think you're bad at maths and would like to help you to figure out how to get the appropriate serving of 4 pieces, i.e. skewers. None of these possibilities work in China, perhaps because people are generally sharp with maths (apparently) or people would laugh at it, just like my wife. 

I was trying to think of a reason for people doing this, apart from filling up the sign or the reasoning above. Anyone got a solution? 

I've got a couple of possible rationales mostly revolving around the idea that they can change the price (which may or may not be possible). Firstly, it's interesting to think of the situation of a stall in a big event like this. They prepare lots of supplies based on an estimate of how much they think they can sell. There is a limited of space to store meat and prepare it. Also price signs like the above can be changed and adapt for changes in the market prices. The key for a successful food stall is to sell them all that you have estimated for the highest price. The first goal is to get people into kebabs and ideally forming a queue, so a low price at least at the beginning is good. Then you need to make sure you set a trajectory to sell all your lamb, and that would be best to have a discount for more. So either raising the one-piece price or setting up a discount for a bulk quantity would be smart. But what happens if you are selling too many, especially at the bulk price? Well, you can either raise the price of both, or you can just make the bulk price no longer discounted. Possible? Probably not, but that's all I got.