Ah -that attribution is from Fire and Sea or Smoke and Ice. From memory, the picture is captioned 'attributed to Hadeland, Norway', which suggests it's an assumption by the author at this stage. I queried it a couple of years ago (because I have the same piece), and no-one at that stage knew either way.
I'll have a hunt through the books for you to confirm that.
Edited to add: Found it. p. 119 Fire and Sea, (Pina and Vigier). The caption is: Hadeland (attributed) teardrop vase with thin diagonal plum stripes.
Because of the 'attributed', it's possibly wrong.