The map doesn't guarantee that at all. Two items on the map can appear next to each other and take a very long time to get between -- perhaps they're separated by a freeway that you can't cross, for example.
That is true, though in practice it would mostly be true that destinations sharing similar travel times and similar directional vectors would typically be close to each other. If you didn't already have some general knowledge of the area, you'd probably notice the complication of a freeway when you "zoomed in" to the standard map view.
Imagine a long river with a bridge at the point you are currently located, but no other bridges. Two places across from the river from each other might each be an hour away, but two hours apart from each other because you have to come back to your current location to cross the river. They'd look nearby on this map because they're in close places and similar times to get to.
This is actually an extremely common case with public transportation:
There are two channels of buses going N-S in the city, and both channels meet downtown. From downtown, two locations can be about equally distant in travel time northwards, and nearby in E-W distance compared to their N-S displacement, but they're separated by a freeway and lie on different N-S channels, and so the E-W distance takes as long to commute (by foot or transit) as going downtown and back northwards would.
That's an interesting and commonly occurring case for this kind of map. I wonder if the visualization would be improved by introducing visual connections between points that are nearby, and/or painting barriers between points that are close in the map but far away in reality.
Two locations that are close to a third location need not be close to each other. A and B might be separated by some barrier which does not separate them from C. Maybe a bit of an edge case, but still, not that uncommon.