In the human brain, information is not stored like cars in a parking lot, with no relation between them, where you can drive away with one car without touching any of the others, but as knots in a network. Thus, a name is stored with connections reaching out to everything that you felt was connected to that name: the tasty italian cookies you ate while you read the book; the body memory of your leg in plaster; the red horse on the cover; etc.
When you happen upon any of the information that is connected to that name – when you eat the same cookies or see someone with a broken leg –, the name will be activated in your memory. The intensity of the activation and if it reaches your consciousness, depends on the strength and uniqueness of the network connection. The color red will be connected to a lot of things and the activation of this particular know will probably be to weak for this memory to reach your consciousness. But someone mentioning Italian pastries on the radio, or getting a whiff of a similar smell, might bring back the memory of your reading.
To know why you remembered the name Holden Caulfield at that moment, we would need to have more information about you at that moment, and about what you did, thought and felt while you read the book. Obviously there was a cue in the moment of remembrance that was stored with the name at the moment of reading or while you thought about the book after reading it. It could have been something you thought about while you were driving and totally unrelated to the actual driving; it could have been a feature you saw (heard or smelled) outside the car; it could have been something on the radio or something your passengers said.
Examples: Someone on the radio says "I'm forever beholden to you." You don't actively listen, but the word is processed subconsciously. Or: You thought about how boring the book was while eating an apple; now you eat an apple and think about how boring the drive is.
Since we do not have that information, all that we can say is that the same cue appeared in both situations.
That you remembered something you had not thought of for eight years does not prove anything about how much information your memory holds. It just proves that the book impressed you in some way – enough to remember the name of the protagonist. Which is why I voted to undo Taal's edit of your question, in which he deleted your characterisation of the book as "strange": "I had no reason to even remember this book because I thought it was boring. It was strange." If you find something strange, then it is out of the ordinary. It intrigues you. And you remember it. Quite simple, actually. (Please undo your edit, Taal.)