BWW is a loosely moderated board. I imagine they have very few moderators, and that they are probably volunteers.
BWW's guidelines, shown in the link below, explain their rules, which are quite often not enforced. Personal attacks are commonly tolerated, but when it comes to threads that could get them sued, they will be quickly deleted when noticed or reported (there's a "report abuse" button on the dashboard that any poster can use to bring abusive posts to the mods' attention(s)).
The thread in question had libelous statements made in it, as did the one created in an apparent attempt to duplicate it, which was also deleted.
They can delete a post, thread or poster for no reason at all. It's their board, provided free of charge. Their board, their rules.
BWW guidelines