First, a very valid reply to there being "at least one anecdote (<-- sp)" is that there is a bunch of actual data on exactly the subject at hand that shows the opposite of the stated hypothesis. You don't throw out or ignore existing data just because one guy on HN got rear-ended!

Second: I think you're being too charitable. I think it's abundantly clear that grandparent believes that there is a "significant risk to other road users", and that this single data point confirms it. And clearly it doesn't.