Hi, the meshes are in the repository in the blender file, it should work. I tried to import the project and the meshes where correct, but someone else has the same problem as you have. Unfortunately, I don't know how to fix it. What version of Unity are you using?
It only seems to extract the blocks.blend into the 'blocks' folder of meshes if you have Blender installed. It failed for me too on a machine without Blender. :)
Unity doesn't actually support .blend files, it will only use an "installed" version of Blender to export the models in the background. If you don't have Blender, or if you used the "zipped" version instead of the installer, Unity won't have any idea what to do with it. I suppose they can manually associate the .blend file with their zipped-Blender folder, but I haven't tried that say for certain.