One thousand is an arbitrary number, and apart from its special place in our base 10 number system is no more special than, say, nine hundred ninety-nine.
I bet that humans at some point will discover thats actually false in the sense that the base 10 system is not completely arbitrary, and brains had an easier time evolving using the base 10 number systems (than say, base 7), and just like electricity flows through the path of least resistence even in other galaxies the same happens with how some areas of the brain evolve, that regardless of their origin they tend to use the base 10 system as well, with some minor differences.
I would be willing to bet that some bases are easier than others, with primes being basically impossible, but not that 10 is inherently easier than 8 or 12.
Yea, but fingers and brains are not strongly correlated. An evolving alien sentience could end up with just about any number of fingers, but most life on Earth has some form of symmetry or other making even numbers more likely. Thus I a can imagine that if we canvassed the entire galactic population, every civilization would use even bases, but there would be no clear bias to 10 in particular. Perhaps a bias away from really large bases, but not one that is in favor of 10 specifically.
I would not discard so easily that brains and fingers are not correlated, I know corvids, dolphins and other species show some level of intelligence but it's nowhere near humans so they are not in the same category to draw conclusions, so the only sample we have is humans, so until we have another sample I wouldn't make any affirmation one way or the other; also we know our advanced tool usage was not only develop due better brains but also due having opposable thumbs.
