" grandparent" was not a choice on my screen, but either "grandma" or "grandpa" would suffice.
This time, "grandma" was not a choice. "Grandpa" was the only choice for translating tūtū whereas most of the exercises will not allow you to equate tūtū with "grandpa." You will be marked incorrect.
I use "tūtū" in normal conversation when referring to my four grandparents (now deceased). Do you mean I've been saying this wrong for the past 66 years and "tūtū" can only be used for grandpa?