Hello Dark_Corvid,
In the thread that you are referring to some additional information is missing:
import Metashape as PhotoScan
doc = Metashape.app.document #active document
ch = doc.chunk #active chunk
Then you can access ch.region, that has ch.region.center, ch.region.rot, ch.region.size attributes.
Note that all these parameters related to the bounding box are defined in the internal chunk's coordinate system.