I agree the rearrangement of the word order is confusing, but I can also see that Musk could have been saying "it is not an evacuated tunnel". (In fact this is the default interpretation I would probably take...) Listening to the original quote could help us, but ultimately there's no way to know if he's talking about tunnels in general or just evacuated ones.
But your interpretation is much, much weaker than "a not evacuated tunnel".
If it's not a tunnel, it's still not an <i>evacuated</i> tunnel.
But if it's "a not evacuated tunnel", then it must be a tunnel.
Edit: Actually, I think with the article "an" between the "not" and the adjective, there is no way in English grammar to interpret the "not" to negate only the adjective instead of the whole adjective+noun "evacuated tunnel". Unfortunately I'm neither a native speaker, nor a linguist, so I cannot back it up with anything but feeling for the language and the fact that this is how I always see it used ;).
> Edit: Actually, I think with the article "an" between the "not" and the adjective, there is no way in English grammar to interpret the "not" to negate only the adjective instead of the whole adjective+noun "evacuated tunnel".
Well, if you add another "only" before "interpret" then you'd be correct. Otherwise, it is open to interpretation either way.
