Of all the elements of the 'other' site, it looks like the only outright copy of your design is the blue header at top. If that was, indeed, made from a tutorial, you would have a very difficult time claiming that it is your "original" design.
If you copied a website from Site Point, that would be plagiarism. Your tutorial would post date their raw files. They could easily prove that they were first.
The point is (about your original question) if a tutorial is available to apply the technique shown in your header, then your header was not your original concept. The originality (ergo the copyright) belongs to the person who first thought of the idea.
To register a copyright you need to put your idea into a tangible form, i.e. on a CD, floppy, in print. However, the moment the idea is applied, the copyright belongs to he/she whom originally developed the concept.