While I can't speak to the popularity of Reddit, I am certain this theory is not correct.
People are legitimately pissed about the constant exposure of their personal data. Exposure not just by Facebook, but by many collectors be it Amazon, Target or Equifax. Exposures that had essentially no consequences for the collectors.
People are pissed and and they let their representatives know. At governmental inquiries all over the world Facebook appears to have bold faced lied about how they operate. Now politicians are pissed.
When the people and their representatives are collectively pissed at something, two things are sure to happen. Firstly, the media will cover it and potentially rile up the various players. Secondly, there will be (at least calls for) fines and special taxes.
IMHO, this collective ire at Facebook has nothing to do with changes to feed algorithms.