Smaller droplets == smaller surface tension?

the physics in these two cases is completely different.

To begin with, soap renders glass wettable, so that any water that condenses on it forms a smooth, continuous sheet that you can easily see through, instead of tiny hemispheres of water stuck to the glass that diffract light.

This has nothing to do with the effects reported in the researchgate article.

Surface tension decreases as droplet size decreases.¹

You can follow the derivation in the source, but the gist of it is:

From Gibbs' equation², we have that in a two-phase system, the surface tension $sigma$ depends on the potential $mu$ as:

$$ {rm d}sigma = -Gamma {rm d} mu $$

where $Gamma$ is the superficial density of matter at the boundary of the phases computed with respect to the surface tension³.

Following the derivation in 1, we get $$ frac{1}{sigma}frac{{rm d}sigma}{{rm d}r} = frac{(2delta/r^2)left[1 + (delta/r) + frac{1}{3}(delta/r)^2right]}{1 + (2 delta/r)left[ 1 + (delta/r) + frac{1}{3}(delta/r)^2 right]} $$

Which can be integrated and simplified (ignoring higher order terms) to $$ sigma sim frac{1}{1 + 2 delta /r} $$

$delta$ is constant over a wide range of droplet size, but varies appreciably when droplets become small enough ($r sim delta sim 10^{-10} {rm m}$)

As $r$ decreases, $delta/r$ increases, and so $sigma$ decreases.