I would explain the difference as: @native says please implement this Scala method of this Scala class in C, respecting all the JVM calling conventions and memo

I would explain the difference as: @native says please implement this Scala method of this Scala class in C, respecting all the JVM calling conventions and memory model. @extern says call this C function that never knew about Scala or the JVM, respecting all the C calling conventions and memory model.