In this snippet, the story of what triggered the memoir is the opener.
Memories can be triggered by all sorts of things—sights, smells, songs, you name it. It flicks something in your subconscious and all of a sudden the memory comes flooding back.
Here’s Ned Vizzini talking about such an experience. Notice that all the detail is about triggering a memory and not about the memory itself. You’ll have to keep reading the memoir to find that out!