I had this experience twice in my life, about ten years ago. I was at a kind of barbecue at a sports club and they didn't have normal barbecues with charcoal, but these stupid things where you pour oil on and fry the meat in it. I noticed they use sunflower oil and lots of it. Ate a steak anyway because I didn't want to be a dick. Don't remember if I also ate potato salad, because they are usually made with sunflower oil as well.
On both occasions I got sick the next day.
So I guess people who usually avoid seed oils are more susceptible when they get a load. After all, other people use seed oils every day and aren't sick every single day. It may be a shock for the system if you aren't used to it.