"What's your mum and dad doing for Pchum Ben?" I almost laughed when I heard my mother in law asked this.
In Cambodia its one of the major holidays, the religious stuff goes for about 2 weeks and the last 3 days are public holidays, many people travel to see relatives. So around this time everyone in Cambodia asks each other what they are doing for the holiday. Its totally relevant to ask within Cambodia but totally irrelevant to ask of people who live in Australia and are not Cambodia.
It reminded me of 2 other questions:
What are you doing for Christmas? (when I'm asked by a fellow Aussie, or other white person)
What are you doing for the summer? (when I'm asked by a fellow expat white person , usually from North American)