Did I miss where he tells how he did this part? Knowing I had left for a run was key to knowing when I had returned from a run, rather than a trip in the c

Did I miss where he tells how he did this part? Knowing I had left for a run was key to knowing when I had returned from a run, rather than a trip in the car for example. From what I see he's assuming a run starts after the phone doesn't respond to ping requests for 5 minutes. How does that imply a run over a car trip?