Is this normal ?

My fiancé has an almost 4 year old nephew. Last time I saw him, last month, he was talking about his penis. He told my fiancé that he’d punch him in his penis (playing around). And then he literally asked me if I wanted his penis.. 😳 UM… NO.

My fiancé just laughed it off. Today he’s back again and still talking about penis and when he play fights with my fiancé, that’s where he’s always aiming. Whether it’s punching him or kicking him, its always the target. I’m not going to say anything but I just want to know if this is normal? Maybe he was just taught about genitalia and is now obsessed with the word penis and there’s nothing else to it? His parents hear him and don’t say anything about it.