The inertial trackers in current-day phones do not have anything like that kind of stability. They accumulate errors at an accelerating rate (they are essentially doing a double-integration of the error).

Using just MEMs based accelerometers, your position error would be hundreds of feet within a minute or two. Gyro and compass can slow the error down a bit, but not enough to be within a road width over 30 miles.

I think it's more likely that GPS was working in the anecdote above. It would be hard to find a place that had 30 miles of road and couldn't get a GPS/GLONASS fix.