What's The Difference Between Thriller And Mystery?

One of the coolest things about writing for kids is when I get to hear from those kids themselves. You'd think that happens very often, but you'd be surprised. Since I'm still new at the author gig, I mostly talk to librarians, teachers, parents, grandparents--those people who will be buying books for the tweens in their life.

So it was cool to hear from a friend who bought the book for his son, but then he told me his teacher wouldn't let him read it for his required mystery book. Since Double Vision is a thriller. This kid ended up reading the book anyway once the assignment was finished (my readers are cool that way). Not that I disagree with the teacher--there are certainly many middle-grade books that are stronger mysteries--but it did make wonder...

What makes a mystery, and what makes a thriller? Is it the puzzle versus the chase?

I do think Double Vision is more of a thriller, so the teacher was right. But isn't it also a mystery? There's a puzzle and a whodunit to solve...

What do you think makes each category? Or is it all just nonsense, this labeling?