It might be one of those "tester" updates that Google frequently uses on a small sample of their database.
It sucks to be the guinea pig of such algorithm micro tests, but it is what it is.
The good news is if you are the subject of such a test, there's a good chance your traffic will recover because it's just a test.
But other times, Google has to tweak or correlate data because their initial algorithm settings might not be up to snuff.
At worst, consider this as a taste test of dark days to come.
At best, use this experience to better prepare yourself for what lies ahead.
Maybe you should interlink your content better, maybe you should revisit your content quality guidelines when it comes to new stuff that you will be publishing.
Whatever the case may be, this may be a blessing disguised as a challenge.