Since there is FCP X, the workflow has never been to directly open a project (you CAN'T double-click on CurrentProject.fcpproject to open a project).
In 10.0.*, projects had to be placed inside a specifically named folder to be seen by FCP X.
Since 10.1, projects exist inside documents, which are called *libraries*. Libraries have the four-star icon, and they CAN be opened by double-clicking, they can be closed, and copied in the Finder to almost anywhere.
In order to use that project, it needs the surrounding structure, not just a file.
It appears to me that this project is from old 10.0.*. In order to update such an old thing - assuming you still have it with the rest of the structure, including the corresponding events - you need to get a copy of 10.2.3 Trial version.
10.3 has dropped the ability to update those old projects.