I’d say that any 16 year old that doesn’t understand sex, or claims to have not seen pornography, is almost certainly either lying or been kept inside and not been allowed to interact with anyone. From a child protection perspective I’d be far more worried about any sixteen year old that has no idea about sex than one that glimpsed a few seconds of a porno during a childish prank by school friends.

What TV shows have they been watching? What social lives do they have? What friends do they have? All the concern here is in the wrong place.