Lettuce, carrots, and celery are all high in water content and low in nutrients, so they are not a suitable diet for guinea pigs. Guinea pigs need a diet that is high in hay and fresh vegetables, and they should only be given occasional treats of fruit.
If your guinea pig died suddenly after eating lettuce, carrots, and celery, it is possible that the change in diet was the cause of death. However, it is also possible that your guinea pig had an underlying health condition that contributed to its death.
If you are concerned about the health of your guinea pig, it is important to take it to a veterinarian for a checkup. The veterinarian will be able to determine if your guinea pig is healthy and will recommend a diet that is appropriate for its needs.