No, it is not normal for a cat and a dog to mate. Cats and dogs are different species with significant biological and reproductive differences that prevent them from producing offspring together.
While it might appear that mating occurred, it could simply be the result of social or behavioral interactions, rather than true mating. It’s possible that one animal was displaying mating behavior, or they were engaging in non-reproductive behaviors like play or dominance.
If you’re concerned about any unusual behavior or health issues related to your pets, it would be best to consult with a veterinarian.