Implicit ClassTag in pattern matching

Let's take this for an example:

import scala.reflect._

def get[T](list: List[Any])(implicit tag: ClassTag[T]) = {
  list.flatMap {
    case element: T => Some(element)
    case _ => None
  }
}

I can use get() to get values of type T from a list (e.g. get[String](list) will give me all strings from that list).

Now, I understand that compiler provides the value of type ClassTag[String] automatically. I also understand that ClassTag is a type class, and somewhere behind the curtain there's a piece of code that says implicitly[ClassTag[T]].getRuntimeClass() or whatever.

But if that's so, how come we can pattern match without the class tag (we just can't differentiate between erased types in that case)? I mean, how is it achieved that, if I declare an implicit parameter (which is automatically provided by the compiler), I get one behavior, but if i don't I get a different behavior?