Which meaning of "big" is implied here?
It could be by age, or size. This is how كبير is usually used.
However, knowing Duolingo and its dialectical influence, they might have implemented the meaning of being (famous). In some dialects, famous is noted as كبير as well.
I wrote "أبي كبير" because I couldn't see the fonts clearly and it was marked as a correct answer (with the "You have a typo" quote) - at December 3, 2020. Thank you!! ❤❤