Hawking is voicing the Dark Forest Theory which most have never heard mentioned.
It goes something like this: Where is everybody? With trillions of suns and billions of planets, where are all the civilizations?
Explanations range from there are none (but us) to everyone else does not use radio (so we cannot hear them).
The Dark Forest Theory goes like this:
You seem alone are in a dark forest, what do you do?
Cry for help and hope that some friendly person comes to your aid?
Do you remain silent because there are dangerous creatures that may hear your call and come to feed?
How do you know of the two possibilities which will be true?
So every one remains quiet less someone comes hunting. Being on more than one world, in more than one solar system increases the odds of remaining undiscovered by hunters.
That is all he is saying.
What about following the flow of water towards larger bodies of water unless you are in a dwarf tree forest?
I think there may have been a lot of intelligent civilizations in the universe, maybe in the millions. But the question is do they exist close enough in both time and space to discover each other? If an advanced civilization had come looking for intelligence on Earth as little as 10K years ago, it would have found none (except for some cave dwellers making paintings and using hunting tools). And 10K years is nothing in the life of the universe.
Based on the dynamics I see here on Earth, I think it is likely that a species will reach technological greatness and then devolve back into sub-intelligence. This could be caused by war. It could be as simple as losing the moral framework that made their intellect possible. In all things with a biological basis, I think the genes contain both the seeds of potential greatness and self-destruction.
“Being on more than one world, in more than one solar system increases the odds of remaining undiscovered by hunters.”
That could be. Or it could also be that just moving around attracts attention. It could also be that having many rabbit warrens in the forest increases the chance of the wolves knowing there are other rabbits in that forest, probably nearby. Wolf finds one rabbit, extrapolates/interrogates to find the rest of the rabbits.
Freegards