agree that 'baking', and even 'roasting', are far more likely terms to describe cooking in an oven than 'grilling' (though that's also possible to do).
also, 'ubi' can refer to 'sweet potato' as well as 'yam', which, for many outside of america, are a completely different vegetable.
We may be using the same English words to mean different things. We Brits grill differently from an American we grill under a grill not over one (for us a grill and grilling is what an American would call a broiler and broiling). If Indonesian use of the word grill is the same as BrE then this sentence would make sense.
from what i understand ubi can also be just purple yam, aka ube. I put that it should be accepted but correct me if ubi doesn't mean purple yam but only yam in general. Ube is often used in Philippine English and even in American English (at least those more familiar with it)