The way we measure gravity is by observing that it behaves how we would expect it to. We don't actually know if this is correct.
The same goes for consciousness, if something behaves how you would expect a conscious thing to behave but you don't know what is causing it can you deny it whilst maintaining that it is reasonable to say the moon has gravity.
The thing we call "gravity" is the the thing we are measuring directly. We have named the mysterious thing that underlies well understood processes and behaviors gravity.
There is no equivalent for consciousness. In most conversations, people aren't even referring to the same thing when they use the word. There is no measurement we are making that we categorize as or attribute to consciousness, so equating the two is a bad analogy.
In fact, taking your statements here at face value, you are equating consciousness and intelligence. A link between the two is only theoretical for all the same reasons your analogy here doesn't work: consciousness is currently entirely unmeasured outside n=1 studies.
The same goes for consciousness, if something behaves how you would expect a conscious thing to behave but you don't know what is causing it can you deny it whilst maintaining that it is reasonable to say the moon has gravity.