Hey @ashish007git,
Sorry for the late reply, I was pretty busy 
If you take a look directly in torchvision.models source code (here 9), you can see some comments that explain that some implementation details lead to a better accuracy.
Beside, if you take a look at NVIDIA NGC 2 you will see that their training routine slightly differs from the one published in the original paper. This way you can squeeze out those last .1%
My understanding is that the pretrained weights from torchvision.models are obtained by performing the training procedure linked above.
Have a nice day!
Alex