Swahili usage of articles is very fluid. "A" or "the" in English is up to the translator and the context. Duolingo is very inconsistent in marking answers "wrong" based on which article is used.
This is a little aside. Simba is Lion. There are no wild tigers in Africa. but they are available in zoos.
No one seems to have an authoritative translation for Tiger. Almost all link to Google-Translate which fails (not in the database), and returns Tiger as the translation.
I finally found this: https://glosbe.com/en/sw/tiger
So, Is it Simbamarara? Is it Chui-milia? Can a native speaker verify this?