It’s not a closed group. You can pull your kid out and put them in a different group. It’s not like public school where your kid is forced to go to the one school in your catchment area.
The parents also have the option of reorganizing the group to kick the bully’s parents out, along with the bully.
I think your article is less likely to have the investigation beginning with the post office and more likely to have affects of multiple regular people not being OK with something, and being present.
Such involved parents could never let anything happen arguments ignore how these things develop as less involved parents cargo cult. (You can't get much more blatant in a drop in actual involvement than the example in the article.)
These kinds of groups connecting themselves to actual home schooling will erode it by association.
The parents also have the option of reorganizing the group to kick the bully’s parents out, along with the bully.