UK here. I don't remember ever getting "the talk" from either parent. There might have been a late attempt that was shut down with "ugh, we learned it all at school already."
Those classes, at some point between 9 and 13, might have cleared up a few school-yard rumours, but I'm really not sure what I knew, what I thought I knew, and what I learned (and unlearned) at that time. It might even have been a year-long, once a week class, but it was a very long time ago now. I don't even remember what the lessons were called, because it wasn't "sex ed". Might have been "Health Studies" or something similarly vague.
As for the subversion of expectation in the OP text, I'm pretty sure we had some lessons on WWII, but I don't think we got into that much detail before I chose to stop studying History. My parents and grandparents certainly talked about the wars, but that was more about them and people they knew during that time rather than the geopolitical and ethical aspects of things. Perhaps a mention of Nazi propaganda from Lord Haw-Haw being on the radio.