Am I misunderstanding the graph in the article? My understanding is that the graph is showing that home prices are still rising, but only at an 8.4% increase between Sep 2017 and Sep 2018 (the rate of increase has just decreased.) If so, this seems incredibly misleading.
Yes, you are misunderstanding it: the house prices are 8.4 higher than in Sep 2017, BUT, they are lower than in, say, Jun 2018. So it is not just "rate of increase has decreased", the absolute values are lower than a few months ago.