Note that the "Level 1" bullet in the rendered document is formatted as a level two bullet, both in its position on the page and the bullet style from template.pptx. The other rendered bullet styles are similarly shifted by one level. There's an open issue related to this on the pandoc development site.
It looks like you may have to highlight the bullets in the rendered powerpoint document and press shift-tab to move them up one level. When I do this, I get the desired formatting and bullet style.