Did you install PyTorch from source or did you use the binaries?
In the latter case CUDA (and other libs) will be shipped in the binaries, so that you don’t have to install a local CUDA version (and it will be ignored).
Have a look at the install instructions 279 and select the command for CUDA10.
I would recommend the conda install command, as the pip install currently might downgrade to CUDA9 even if CUDA10 was selected as tracked here 57.