Any idea how exactly the 6D, 5DIII & 60D achieve 420fps?

According to this, these cameras can shoot slow-mo movies at 420fps:



Shirley some mistake?

I was looking for a large-sensor camera which can shoot low-res movies at 120fps or faster...these were the only ones that came up.  But they don't go faster than 60fps, unless I'm missing something?