THE PLOT THICKENS!
I reimported the file because it seems to have been somehow corrupted by applying it as a texture for a quad image file.
Steps:
1. Import the file fresh, it's pixel perfect beautiful when I drop it into the scene.
2. Drag it onto the buttons quad image I made
3. Drop the image into the scene:
There's the inspector. Toggling the Override and changing options doesn't do anything. I'm going to try deleting and fully remaking the quad now to see if that fixes the issue.