Hey, I see what you mean so let me respond with my explanation of the statement that these two are different experiences:
Tom Campbell’s and Robert Monroe’s models are reality description models where they describe all of the existence as one stream/scale of consciousness with different focus and/or frequency levels. The focus level defines what “reality” you find yourself in.
As the ultimate truth I believe that this model of existence is correct since consciousness is the only real thing and everything else including all the different worlds and realities are just projections of this consciousness.
Now with that argument, for distinguishing between different experiences like lucid dreaming and astral travel, but also all other experiences including being in the physical body, you would always end up with such a reality model since there is nothing else there but the scale/stream of consciousness. With that model and definition all experiences would be pretty much the same and would have just simply a slightly different focus 
With that model alone your physical reality is then almost the same as lucid dreaming, astral projecting and all the other possible worlds.
From a practical point of view however, it makes sense to distinguish further between lucid dreaming and astral travel. Also because we as currently physical humans and cannot grasp the full scale and stream of consciousness. And also because we want to have a clear distiniguishment of the physical world, the lucid dream world and astral worlds, for practical reasons.
Now with lucid dreaming your stream of consciousness is mostly going into an INTERNAL WORLD created almost exclusively by your own current subconscious mind configuration.
With astral travel your stream of consciousness is mostly going into an OUTER COLLECTIVELY SHARED WORLD created by you but also Quintillions of other beings with different levels of manifestation power and skill level.
Hope that explanation makes sense to you.
