The System Information panel in the system settings is not getting the value from the hardware, as lspci does, but is getting information from the userspace drivers for Xorg and OpenGL. As a result, depending on which drivers are being used, the requisite information it uses may not be available. In this case, it defaults to displaying Unknown rather than the name or type of your graphics card.

More accurately, the panel tells you what graphics system you are using, and not what graphics card you have.