That briefly boosted the demand for GPUs (until much of it switched to ASICs), but the existence of GPU compute in the first place came from gaming and NVIDIA's choosing to implement programmability the way they did.

The existence of cheap parallel processing was certainly a necessary enabler for large neural networks to take off.

I don't know who else may have experimented with using GPUs for neural nets before 2012 (not so easy since it required hand coding everything in raw CUDA - no framework support), but AlexNet drew a lot of attention (it was a very dramatic win of the ImageNet 2012 competition - the first neural net entrant, and a win by a very large margin), and large neural net research just accelerated from there.