I agree with the technicality.
Otherwise, the soap you buy from the store would be a puddle by the time it got on the shelf.
I've got hotel soap from vacations 10 years back still bone dry, stored in the bathroom yet.
Good demo of hygroscopic is a crystal of pure sodium hydroxide left open to atmosphere. Got to see to believe.

A good point was made that I'd never considered about soap reacting with the wood and leaching resins (as a solvent), later affecting the coating.
What others might do this? The turp in a turp/wax mix, the petroleum distallates in hand cleaner, etc.?
What about pH changes?

And how do I make sure there's no stray anything left on the wood when I'm done? All would seem to block a finish.

big snip
Soap may be somewhat hygroscopic, but better examples would be methanol and
ethanol. They absorb water from the air readily. Perhaps the property
you're thinking of is hydrophilic or hydrophobic. Soap molecules have a
hydrophilic (water-preferring) end and a hydrophobic (oil/fat-preferring)
end, which is why it works as it does by cleaning a variety of substances.