I downloaded the SVG and opened it in Inkscape.
Problem 1 is the ID as vanepp said. The board needs to be in a group with the ID “board”.
Problem 2 is the page size is not set to the same as the object. In Inkscape you go into page properties and set page size to match the selected object.
I have copied the path into a new Inkscape SVG and made the changes for you. If you want a silkscreen layer you will still need to add it as another group called “silkscreen”(top silkscreen) and/or “silkscreen0” (bottom silkscreen)