PointTransformer Test result with pre-trained model on S3DIS dataset

### Checklist

- [X] I have searched for [similar issues](https://github.com/isl-org/Open3D-ML/issues).
- [X] I have tested with the [latest development wheel](http://www.open3d.org/docs/latest/getting_started.html#development-version-pip).
- [X] I have checked the [release documentation](http://www.open3d.org/docs/release/) and the [latest documentation](http://www.open3d.org/docs/latest/) (for `master` branch).

### My Question

Thanks for the work! I have a question about the test result of PointTransformer(pytorch) on S3DIS dataset with the pretrained model you provided.
I tried to do the test on Stanford3dDataset_v1.2_Aligned_Version and Stanford3dDataset_v1.2.
I get mIoU 67.35 for aligned version and 67.79 for the other one, never get 69.2 that report in the table.
Do you have any idea why?
Best,
Pan