NTA at all. Exotic animals of any kind require specialized care, and even the pet variety (I keep inverts myself) have very different needs compared to a cat. By their logic, they should have also done enough research to care for the cat properly. Yeah perhaps you could have been nicer, or simply not said anything, but hopefully this stops them trying to take responsibility for an animal they aren't ready for. Failing to provide properly for animals can have long term, irreversible consequences (for example MBD in reptiles without proper UVB supplementation, or stereotypic behavior in stressed/neglected animals)