a brand of poultry is labeled with information that says the bird was fed only a vegetarian diet. What does this suggest?

The bird consumed only plant and dairy/egg products and did not eat any kinds of meat.

Explanation:

This suggests a healthier animal, and, in theory, high quality meat overall. By having the bird take part in 'clean' vegetarian eating (which is different from vegan, where the bird would have eaten no animal products whatsoever), it suggests the meat would be better in taste and healthiness for the human consumer.