I ran into this issue as well.
I threw a Dinner Party and served a Grand Breakfast and called everyone to eat.
That worked normally, but as the party went on, another Sim must've gotten hungry, but instead of grabbing another serving of the Grand Breakfast, she went to my Sim's fridge and pulled out some leftover Plasma Fruit Salad.
But she wasn't a Vampire, none of the guests were, so of course this made her sick.
Non-Vampire Sims shouldn't autonomously choose to eat Plasma Fruit Salad.
Or at the very least stop after the first bite.
