By default, PowerDVD will output the image in its anamorphically squeezed format, which is how it is stored on the disc. Your display unsqueezes the image to make it widescreen. So, here, PowerDVd uses the "Original Video Window Size" option.

Instead, use "Current Video Window Size" and check the box to maintain aspect ratio. That will dump out the screengrab in the displayed rather than stored format.