I'm not sure what the "rent related phrases" are but just looking at the trend chart for "rent" reveals a similar pattern [1]. "Numbers represent search interest relative to the highest point on the chart."
My problem with it is a bit more basic: why bother showing stats on Google searches as an "indicator"? Why not just go straight to the stats on rental demand vs. supply?
That chart has no y-scale, so it's impossible to tell if it means anything.