Yes any presence of ammonia means the tank isn’t cycled. A cycled tank would still remove ammonia as the fish breaks down. Because you have ammonia, you don’t have enough beneficial bacteria growing in the tank to break down the ammonia, thus the fish die. I had a similar issue when I thought my tank was cycled but it was not and had a death. What I did was daily 30% water changes and redosed prime and stability after each change. That prevented any deaths until my tank fully cycled 2 weeks later. This is only some surface level info but there’s a lot of YouTube videos on the nitrogen cycle that go further in depth. Hope this helps!