I think there is a connection between the two because if we are ignorant of something we tend to be stupid about it or act stupidly, because we are ignorant of the facts or truth.Stupidity isn't ignorance
Take for example about how some people vote. Many people vote against something that could be in their own best interest, like universal healthcare or gun control.
Kant talked about the ignorance of the masses. I think he was also taking about the stupidity of the masses. And I don't think he felt that would change much over time, thinking that people would remain ignorant and stupid. That's why I think he believed in a strong and all-controlling state, like that in which he lived, Prussia.
The world has changed, though. We are not as stupid as we used to be. And because of that the power is now more in the hands of the people than the state. Moreover, it's the mass education promoted by the state that has made most of us less ignorant and stupid, and more in control of our lives.
Yet there are people who think that on mass humans are still stupid. But I think that sentiment comes from the idea that by now we should be living in a perfect world but we are not.