I wouldn't say grooming but it is a weird relationship. She is an adult woman (20-21 years old) and he is a 15 years old teenager, from her point of view he should be like a little brother to her no matter how mature he seems.
I think the isn't grooming as the 15 year old male started the thought of a relationship and the 20(?) year old female is putting on breaks until he 16 (assuming her prefecture age of consent is 16)