The comment is used to express a celebration-like attitude about an event or blessing. Christmas, Birthdays and Diwali (Hinduism Diwali is celebrated in the honor of Lakshmi, the goddess of wealth) are all seen as events of celebration and joy. To be very hungry and then find food to eat is being seen as a great gift and blessing by the boy. It does not have to actually occur during Christmas, Diwali or his birthday. The event simply feels that important to him and, as such, he uses them as a comparison.

Christmas and Birthday are both special days you receive presents in the US. I am only guessing that Diwali (a holiday in India) is also a time you receive presents as well.

I will add that what he says is (accidentally or deliberately ;) not natural English. It should be 'my birthday'.

maybe he can only eat so delicious food in these festival, so he is so excited.