He's talking about physical constants, to which Benford's law applies (since we expect the first digits to be distributed the same when stated in different units, e.g. meters and feet, we expect there to be the same number of constants that start with 1 in meters as those that start in 3, 4 or 5 in feet (since 1m=3ft, 2m=6ft), etc').

In any unit you choose, about 30% of rivers on Earth and about 30% of public company market caps will start with a 1. This has nothing to do with people's preferences and everything to do with scale invariance.

I certainly read it as applying to both. Certainly Benford's law is demonstrable in many areas, but there's also an interesting sort of "Benford's paradox" at play that when free choice is given between units options, people seem to "prefer" the versions of constants with the lower starting digit. An interesting question of whether one seems more "natural" than another simply because Benford's law so often applies to similar situations.