"..Not stupid but ignorant."... Ok, that's your opinion.
No it's not.
He engaged with them. They quoted "facts" which were simply wrong. When told they were wrong they fell back on their "opinion."
If ignorance is "Lacking knowledge" (look it up) then their ignorance (people he's talked to, not every Leave voter) is a fact.
Can you not tell the difference between ignorance, stupidity, facts and opinions?
That would make you a pretty typical Leave voter.