The issue is that the "young" demographic mentioned in the article is ages 18-29, and high school must have changed quite a bit in recent years if students have not actually heard about the holocaust or WWII.
We learned a lot about early Canadian settlement and relations between Europeans and First Nations. By the time I found myself in high school we only needed to take a certain amount of "social studies" credits and, while history was included in that category, there were options that were not specific to history. My experiences learning about Canadian settlement had been so dry and boring that I had made up my mind that I didn't like history at all and so I made every choice in high school to opt out of having to take history classes. In other words, WWI and WWII, if they were taught at all were "optional."