They copied strings, and visual design. Both of which are work, both of which are covered by copyright.
The elements of a design that are ornamental, utilitarian, or a general look and feel are not covered under copyright but would be covered under a design patent if one exists.
Strings are only covered under copyright if they are a sufficiently original work of human expression. Simple informational messages generally wouldn't qualify.
If I take the first chapter of Harry Potter and write a new ending, it's still copyright violation. They took many parts.