I am currently watching lesson 9 and there Jeremy talks about the transformations in the “Bbox only” section in the jupyter notebook. As you can see at the transformed/rotated pictures of the woman the bounding box is not rotated and is only resized (and still aligned vertically and horizontally).
I guess to rotate the bounding box you have to adapt the class “CoordTransform”.
In addition, you have to use “tfm_y=TfmType.COORD” to transform the coordinates of the bounding box too.
However, maybe the pixel transformation can be of use with TfmType.PIXEL (see class “TfmType”, should be covered in later lessons on image segmentation).