Well, the problem with this explanation is the cabbie must have been out front of the Buchanan house because he saw someone (obviously Kim) run out from around the house and get into the car, arguing with the boys.
Another possible explanation is that the cabbie Mostafa NEVER PUT HIS FLAG DOWN until a few minutes later. He said he sensed it was a bad scene and told the boys to get in the car so they could go. In all the fluster and commotion, it may have been a few minutes until Mostafa noticed he had not started the meter running. It may be the time recorded as when the meter started (1:07) that he is relying on.