You missed the sha-1 collision: https://news.ycombinator.com/item?id=13713480

Besides the two Uber stories, it's simply that a large number of incredible events have happened recently. If you'd have told me about the sha-1 collision, Cloudbleed, S3 going down, or the seven exoplanets, I'd have predicted 1K+ votes for any of them, simply because they're very newsworthy, relevant, and super interesting to HN readers.

The two Uber stories hit a nerve in a hot topic, adding a lot of specifics to formerly vague concerns/accusations. If you'd have shown me the stories before they were posted, I would have predicted "front page, probably in the 200-400 range", rather than the 2K+ votes they each got. Either they were very lucky, or (more likely) my model doesn't account for that particular type of story.