Behavior economics, irrrationality and my eid shopping!

Today, something interesting happened. The story needs a little background... The next day according to the Islamic calendar happens to be the Eid day here, the biggest festival for the Muslims. Therefore, it's a big holiday in the national calendar, when people (not all but many!) usually leave big cities for their ancestral homes to spend the holidays with family & friends. The cities generally take a quiet and deserted look and it's common for shops and businesses to remain closed for 3 or 4 days at a stretch. On the other hand, the festivity of the day demands people to prepare exotic and rich menu of traditional foods to offer to the relatives and friends. So, you see, there takes shape an apparent gap between the demand and supply (lack of supply as many of the shops are closed vs. sudden spike in demand of consumable goods). Naturally, this opportunity to make some quick bucks does not escape the attention of some unscrupulous shop owners. So... maintaining tradition, today was also no exception and milk (one of the essential items for preparing Eid - day foods) experienced a sudden hike in price in my neighborhood grocery. I had to buy some... when I inquired the price, I found the grocer was asking 20% higher than the usual rate. (I was irked, but what could I do! so I kept my peace!!). Now there is this particular brand of milk that usually costs 10% more than the general categories. So, next I inquired price of this superior category, and to my amusement I found the shopkeeper in his haste forgot to increase the price of this brand. It was being sold in usual rate. Which means the expensive one (& supposedly the better-quality one) is now cheaper than the 'cheap' one. Now, here comes the interesting part... I was supposed to buy a certain quantity of milk, beyond that amount I really did not need as then I have to store it for future, which not a particularly attractive option... But, seeing the expensive item suddenly being 'cheaper', I bought substantially more than the amount I required! Moreover, it gave me mental satisfaction (I felt smarter and superior!) seeing others were not noticing this simple fact and were buying the usual one at a higher price than mine. This prompted me to buy even more of the milk than I needed!