tldr: it was a very radical idea and he was a difficult, unliked man. I read that as "kind of a jerk", but that's my interpretation. We might react the same way if the person you dislike for being a smartass comes with an idea that there are invisible tiny things killing people.

I think there's a lesson here, it's not enough to be right. You need to sell your ideas well. Especially if you're selling to a group that already dislike you due to previous interactions.