Come on, no one even knows how big the universe is! (Astronomers are yet to find the edge of our universe). So basically, you have no idea how many atoms are there in the universe in the first place. So, comparing the number of atoms (which is an unknown quantity) with the number of chess positions is a little absurd.
Don't know who made this statement, but I'm sure he wasn't an astronomer.
Indeed, chess are Universe and the pieces are Galaxies.