They have a design in a style that's not quite originally theirs-- they've seemingly abused the DMCA to have github remove a completely unrelated UI kit in the same style.
The two items in question are as follows: https://layervault.com/ http://designmodo.github.com/Flat-UI/
Flat UI has (seemingly) been designed and developed completely independently, having nothing to do with LayerVault. No artwork is derived, based-upon, designed by the same artist, etc.
You should care about this because the process is biased towards the accuser. Given no chance to rebut, Flat UI is removed, and disabled. Despite providing his side of the story in the commit comments https://github.com/github/dmca/commit/735e17614cca63102b8414..., the author now has to write a formal counter-takedown notification, and the repository will still be offline for up to 10 days (https://help.github.com/articles/dmca-takedown)
Furthermore, 'designers' and HN users should care because LayerVault runs a 'Hacker News' for designers at https://news.layervault.com/. LayerVault is not the right entity to run this site after these DMCA shenanigans (if in fact no infringement has taken place).