Ok turns out it was another mod that deleted it. But to explain - another poster posted a list of bullet points about the documentary which were pretty controversial. This led to some fairly strong reactions and took the topic off course as people were discussing the poster's views rather than the documentary.
The bullet points were deleted and so was any discussion of them which quoted that post, in order to tidy up the topic and make sure it didn't kick off again.
So nothing wrong with your comment, it was just deleted along with many others in an effort to get the discussion back on track.
Hope that helps