Section 16.9 <style:master-page> says:

"In drawings and presentations, master pages can be assigned to drawing pages using a style:parent-style-name attribute."

In this sentence 'style:parent-style-name' was probably meant as 'draw:master-page-name'. A master page is not a similar type of style as a drawing-page style, so allowing a master page to be a parent of a drawing-page style would have complicated behavior which is not currently specified.

Also, the erroneous sentence talks about assigning master pages to drawing pages, not about assigning them to drawing page styles. 'style:parent-style-name' is an attribute for style:style, while 'draw:master-page-name' is an attribute of 'draw:page'. Setting draw:master-page-name on draw:page is the appropriate way of assigning a master style to drawing pages in drawings and presentations.