Maps on iPhone gives me completely wrong distance estimates
This is just a speculation and based on observation, but it seems that Maps will use the last place the iPhone "checked in" as point where it thinks you are to calculate distances.
When you click/tap on the specific entry, it then gets the actual GPS coordinates to then draw the map/calculate directions.
The way I solved the issue was to search for my place of interest in Bing (yeah, the Bing App) because it gets the actual GPS coordinates, runs the search, and then hands off to Apple Maps.