What does it mean if someone says i dont know who you are ive never met you before please dont talk to me or message me back and is thid person immature?

Maybe he/she doesnt trust you because he doesnt know who you are, never met you before that's why he doesnt like you to talk with him or don't message him back. I can say he is maybe immature if he is young I can prove it because it happened to me on facebook. I message someone a cute lil boy bcos I like his face but then again at the first time it is ok but at last he said I don't knw you please leave me alone. It is better for them not to be disturbed them with some strange people who they doesnt really even know better.bcos he is eleven years old only so he is immature or inexperienced around the world. But if he is at the right age maybe he doesnt want to talk to some people he really don't know or like that, for him that's a waste of time.