Nvidia made the first gpu because nvidia coined the term gpu. Its about as relevant as saying ati made the first Radeon video card.
Actually you are incorrect Nvidia made the first GPU because it did all the graphics processing that is why they called it a GPU.
Before the CPU did most of the graphics processing with the help of a accelerator card.
The World's First GPU
http://www.nvidia.com/page/geforce256.html
August 31, 1999 marked the introduction of the graphics processing unit (GPU) for the PC industry—the NVIDIA GeForce 256. The technical definition of a GPU is "a single-chip processor with integrated transform, lighting, triangle setup/clipping, and rendering engines that is capable of processing a minimum of 10 million polygons per second." - See more at: http://www.nvidia.com/page/geforce256.html#sthash.IhrU5XwX.dpuf
The GPU represents a significant breakthrough in realism. It literally transforms the way you interact with your PC. It accomplishes this by completely offloading all graphics acceleration from the CPU. - See more at: http://www.nvidia.com/page/geforce256.html#sthash.UcJJZXT0.dpuf