Hi Psygorn !

I don't know how Zooen done it, but this method is a possibility...




I drew a profil for the vase.


Made the vase by rotation (no cap)

I the vase cut to have something like you had (the top part)

With the same process seen before, I did a loft object with multiple curves (here in green)


I flow a Voronoi set of objects on this lofted object.


I use the vase (total vase, so perhaps have you to redo it because it has been cut before) with a Offset /Shell to have a volume
Next I use the new voronoi set in a boolean operation (difference) to make the holes.

I finished with some softerizer actions, fileting the holes and blending the top to have soft border .

Not so far from Zooen result.
Zooen's version is a slim vase, mine is a fat version.