This is purely anecdotal, but some of the most prominent notifications FB sends me is when someone who's been inactive for a while posts something. For example, I had one friend who posts maybe once or twice a year, and I would always be notified if that person posted something new, like when he suddenly posted an album of his recent vacation to Europe.

With that being said, the FB algorithm beast is far too complex to figure out by guessing, so experiences like the one being outlined in this twitter post are probably all too common.