There's no reason for this as the design was due to the topography of the area, NOT some idea about promoting Muslim beliefs.
I DO happen to know that the symbol of Islam looks like...
The one's calling the design the "Crescent of Embrace" are those promoting the petition against the memorial. The U.S. government is NOT calling the site the "Crescent of Embrace."
Those against the memorial are editorializing the idea just by calling it "crescent" and emotionally charging the issue.