This is not true, bunnies unlike other animals are extremely territorial. In the wild, they have their colonies and do not allow other colonies in. What this results in domestic rabbits, is deadly fights. Bunnies can be bonded to other bunnies. This process can take anywhere from a month to 6 months to fully bond a bunny to another. These bonds can be broken as well if not maintained, or any environmental changes .Bunnies who are already bonded, will forever need a bondmate. Rabbits who lose their bond mate can go Into depression, which will result in them refusing to eat or drink, and sometimes even dying.
Bunnies can be bonded to other species
Bunnies do have a very low tolerance for stress. This can result in them having a very high likelihood of having a heart attack.
Introducing them to a dog or cat needs to be taken with extreme caution, not only for the cat or dog attacking the bunny, but for the bunny's stress level.
You will want to slowly Introduce the bunny to the animal, with the bunny In a kennel, and you in their with them to watch their breathing and stress level. You never want to let the other animal chase, or touch the bunny until they have gotten used to the other animal through the cage. Even then, only while supervised.