He wrote a post based on legal considerations and upon his domain knowledge. One of the interesting things about domain knowledge, or, more to the point, lack thereof, is that without any, one cannot know the exact extent of one's ignorance of other domains.
I am not going to go so far as to assert the author was heretofore unfamiliar with the concept of a zero-day exploit, though it seems likely, but I would suggest that the author is now at least notionally familiar with the concept - and has written quite a good, clear follow-up article devoid of our jargon (which is easily among the worst of the several domains I've been exposed to over the years) indicating exactly and precisely why he reconsidered his position.
THIS IS HOW KNOWLEDGE WORKS. Forgive the caps, but they are appropriate in this case. If we waited for everyone to know everything we think relevant before they wrote anything at all, all we would have written would be recipes. And pornography.
A domain expert wrote a reasoned piece based on their domain knowledge. Others helpfully directed that expert to domains relevant to the piece. The domain expert then (quite speedily, I think) absorbed just enough of that domain's knowledge to draw and state reasonable conclusions.
This is also how the law works, which is why it is so maddeningly slow sometimes.
Editorial or "meta" notes: I upvoted because I don't believe in downvoting (I often upvote downvoted comments for this reason) - but I believe you were downvoted because you were lazy and chose to post ad hominem comments without due consideration.