I took a Denotational Semantics course in college in the 80's. I was completely lost, despite going to class every day and trying to understand what they were

I took a Denotational Semantics course in college in the 80's. I was completely lost, despite going to class every day and trying to understand what they were teaching. I got a 37% on the mid-term and thought "holy f, this is a class I am not going to pass, wtf is going on?" I went to the prof during office hours, explained I'm confused, he asked to see my mid-term and exclaimed "Hey, you got the highest score!" To this day I can still see the gray skinny little textbook with the title "Denotational Semantics" and I still wonder "what the heck was that course about?"