"3-D graphics systems maker nVidia (NVDA) Tuesday unveiled its next generation graphics accelerator, which it hopes will deflect some of the attention from new console gaming machines. The GeForce 256, which nVidia calls the world's first graphics processing unit, will be the successor to its TNT 2 line of graphics chips."
> https://money.cnn.com/1999/08/31/technology/nvidia/
Reading deeper, it seems like Nvidia considered it the first because it was the first GPU to ship with hardware accelerated T&L:
"GeForce 256 was marketed as "the world's first 'GPU', or Graphics Processing Unit", a term Nvidia defined at the time as "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"."
> https://en.wikipedia.org/wiki/GeForce_256
I would also consider earlier NVidia parts like the TNT2 to be GPUs, personally, not sure I agree with this claim either. I certainly called my TNT2 a graphics card back when I bought one in the 90s.