It seems strange but really it makes sense

The outbound flight leaves at 09:35 but by the time you are air born and the food is ready to be served, its lunch time, so they serve you lunch.

Then when it lands in Chennai at around 01:00 they can't serve you another main meal, and its closer to breakfast than anything else, so thats what you get.

For the return, it leaves at 04:00 and so you get breakfast, which isn't the main meal. It then lands at around 09:00 and you get lunch because they already served you breakfast.

You still get your main meal and the smaller meal

i've done this journey 8 times now, always gets me very tired though as its further than you think