Zillow pricing inconsistency

[German E.]

I am not here to complain about Zillow giving an inaccurate Zestimate value - I know it's a free tool and it assigns a value to almost each home in America so one can only expect so much.  But I noticed that lately there is a baffling internal inconsistency in the website.  When you look up a house eg in Southern California or Philadelphia, the Zestimate history graph of a city has been fairly consistent in the past few months, stable or even doing down in the past 12 months.  On the other hand, for the same house if you scroll down you see the "Zip code stats" describing a blazing hot market going up by 10% or more in the last 12 months.  What is going on??

The Case-Shiller home price index has shown huge gains for most urban areas in the last 12 months, by 10% or more.  This is very important information for investors.  Redfin estimates are also much higher now than a year ago.  I wonder what's happening to the once trusty Zestimate, whether it has gone off the rails or I'm missing something. Thoughts?