Wood, especially new wood, has alot of moisture and when that mositure evaps, the wood has to shrink. Shrinkage is a natural thing and it would occur as you stated with or without the humidifier to an extent.
Wood will seek an equilibrium and stop. This is the ideal time to caulk and make adjustments.
I am not jumping on either wagon on this issue, I am just stating that some of this would happen regardless.
That is why when you lay down new flooring, wood flooring, you want the bundles of wood to be there in the home for a good week in advance and stack the lumber in a manner where all the sticks are allowed ventilation. This reduces the shrinkage and expansion when on the floor.