Ex sending our son to school with smelly lunches

Me and my ex husband have split custody of my 5 year old son. He gets him one week. I get him the next. My ex husband is Korean. When he has his week with our son for lunch he just packs him left overs from dinner. Its my week with our son and when I dropped him off another mom approached me really angry saying that some of my son's lunches stink and it makes her child lose their appetite. She told me she's complained to the teacher, principal, and nobody will do anything about it so I need to. I was so embarrassed and called me ex to tell him about it and he could care less. He said her kid can just not sit by our son if they don't like the smell but he cooks Korean dishes and he doesn't like to waste food. I said he could make him other lunches like sandwiches or something and he told me I can either send our son to him with 5 premade lunches for the week or that lady can kiss his ass because he doesn't care. It's apart of his culture and our son loves it. Which is true. My son adores kimchi and other Asian foods. I started to worry our son may get bullied for his lunches. Luckily when I spoke to him he seems really happy at school and have a lot of friends. But I don't understand why he has to make this a thing and can't just make our son other lunches. I'm extremely embarrassed and do want other moms to like me so I can make mom friends. I also don't think it's fair that I have to send our son with 5 premade lunches just so he doesn't give him stinky lunches. My ex has already made it clear he's going to keep giving him lunches from dinner the following night and if some of them a kindergartner doesn't like the smell to them oh well.. This is embarrassing.