I agree that his opinion should be taken with a grain of salt since the topic is far from his field of expertise, but I don't think it's reasonable to expect someone to do literature review before posting an opinion to a social media website.
Are you implying it "ain't" ground truth because it's not perfect? Ground truth is simply a term used in machine learning to denote a dataset's labels. A quote extracted from the link that you sent acknowledges that ground truth may not be perfect: "inaccuracies in the ground truth will correlate to inaccuracies in the resulting spam/non-spam verdicts".