Overall Testing Accuracy and mIoU on test set of SemanticKITTI using KPConv

### 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 `main` branch).

### My Question

Hello, i have tested the kpconv for semantickitti, just for 2 sequences (14 and 17) and i get very low mIoU and accuracy.
sequence 14: Overall Testing Accuracy : 0.3673319553580051, mIoU : 0.26943412959107105
sequence 17: Overall Testing Accuracy : 0.3573021415390024, mIoU : 0.2095614369660527