I would seriously avoid making a big deal out of it.
It's good he talked to you. You need to keep that communication open. If he sees you getting agitated then he'll view the whole subject as naughty or "something we don't talk about".
Haven't rtft so apologies if you've already said but have you asked your son what he was actually told? Kids can get things very wrong. It's our job to correct any misinformation.
I wonder if you are feeling more miffed because you're not keen on the child. Would you have been more relaxed if it was a lovely child who you felt was a good boy?
Regardless, I personally think it's a little outdated to have this huge emphasis on "the talk". I've always felt answering questions appropriate to age (and instigating casual conversations if a situation presents itself).
That open dialogue has been invaluable for the teenage years and new relationships. All very casual (normally on a drive!) but massively important as they navigate their way through the different stages and emotions.
Infact it has been me talking to my DS throughout and DH said he'd never actually had "the talk" with him. He didn't need to...!
I think what i'm saying is, it's about gradual conversation.
If you close down a conversation or panic, it could make you unapproachable.