Difference between 'stupid' and 'ignorant'

Friday in Quest I spoke of Viktor Frankl and his time in Concentration camps, and of seeing his wife and parents killed there, and the terrible conditions that were in these camps.
One of the boys, a first year, said 'well, they shouldn't of gone there'. I had to explain that it wasn't a holiday camp, and then went into a bit more detail.
He wasn't stupid, but ignorant. He had never heard of a concentration camp. I, on the other hand, should of explained it better than assuming everyone would know about something 60 years ago. That is stupid.