You have to watch it a bit closer. He didn't ask for the problem to be explained in simple terms because he didn't understand what was going on. Instead he wanted to make sure his subordinates understood the problem and didn't try to hide their ignorance behind needless complexity. This is a strategy used by all of the most effective managers in the real world ("pretend that I'm stupid", "explain it to me like I'm five"). It was clear from the get go that he was the smartest person in the room in every scene he was in.
The movie also makes clear multiple times that the only people who were surprised by what was going on were the little guys – risk analysts and middle management. People at the top got the news and were simply like "ok guess it's finally happening".
If you ask around people who do this stuff for a living, all of them will tell you that out of the dozens of movies about the financial crisis, Margin Call was conceptually the closest one to how things actually work in the industry (obviously disregarding the Hollywood-esque dialog and characters).