My opinion regarding what beliefs`dang holds is that the 'Idea Sunday' was consistently earning karma disproportionately to it's contribution to the quality of HN and that this was creating a genre of similar high reward high noise threads [e.g. Screenshot Saturday, Tweet Tuesday etc].
My guess is that he looked at the threads closely before pulling the plug, not only because his post implies it but because it was allowed to run for several weeks before he stepped in and moderated. By the time action was taken a fairly detailed picture of who was looking at and participating in the threads was available.
Is it the call I would have made? I don't know because I'm not charged with that, (though I did flag this thread because of its poor quality) and I haven't seen all the facts.