Does a displacement of the meniscus root mean a tear?

Most likely yes. Often there is not consistent terminology used when reporting MRI results. Different words describe the same thing. The meniscus root is where the meniscus is solidly attached to bone in the front and back of the knee. Meniscus root injuries usually occur at the back attachment point. If this root is "displaced", it likely means that there is a tear allowing the root to move out of position.