This question already has an answer here:
Why does every time anybody referring to a Hindu cultural thing says it's Hindu mythology?
Because "mythology" means:
Mythology is a collection of myths, especially one belonging to a particular sacred, religious or cultural tradition of a group of people. Myths are a collection of stories told to explain nature, history, and customs–or the study of such myths.
Hindu culture is based on strong scientific evidence. Although people call Lord Rama as mythological character, recent scientific studies proved the existence of Lord Rama and his vanaras.
As all of this is a scientific fact that we don't tell others, so please don't refer to Hinduism as 'mythological' in any manner.