Is it normal for a boy to tell your sister that he likes you?

Okay, so one day when me and my sister was at school, she told that this boy had a crush on me. I asked who, and she told me that it was someone in my gym class. I didn't believe her at first until she described his appearance and everything. Every since she's told, me I notice that every time he's sees me in the halls or in gym he stares at me wiredly. Now that I know, I just wondered why did the boy tell my sister instead of telling me? Is that even normal?