Strange gmail issue, you think you deleted something, but it was not!

OK so I had a conversation with a friend back in late November about some guy (Jordan Peterson) I saw presenting an interesting lecture on YouTube, he responds to me saying he appreciated that person too and suggested I look up another speaker whom he refers to as an "intellectual". Now, for some reason, although I saved that email as I was looking forward to looking up the person he referred to, this email has dis-appeared. When I search up for the emails in the inbox or the bin, by searching for the word "intellectual" it brings up the actual conversation thread. Oddly however, the actual email in which he names the person I am looking up, is not present. So how is it gmail knows that is the thread that I am referring to because it obviously contains that word, yet it does not present the actual email this word was contained in?