Does bacteremia cause meningitis or is it the other way around?

Yes: Bacteremia can cause meningitis

Words matter: The blood is the bodies resource highway. The "emia" means the germ would be on that highway. Meningitis can result when germs travel there in the blood, or by near direct extension from the soft tissues in the nasal passages or a penetrating injury to the brain. Once there it may or may not ever enter the blood.The term bacteremia is generally used when there is evidence that it travels in blood