DS is 8 in Year 3. He has told me some things that a friend (same class) has told him. The first incident was when DS asked me what spunk was? After choking on my tea and asking about context he said X told him about it. X said spunk comes out of your willy and you put it on girls faces, boobs and bums. 
Second incident in the car yesterday, DS pipes up that X has told him that if his mum is nasty to him he is going to stick his balls up her arse

Obviously, this has led me to have conversations with DS that go way beyond your average sex ed chat. Thankfully he's very naive and was quite uninterested.
X has older siblings, which is where I assume (hope) this language is coming from.
WIBU to mention this to DS's teacher as something to watch out for as I feel this is age inappropriate sexual language or am I being naive and this is the norm for 8 year olds (please tell me it's not).