Is it possible the toll booth operator is scamming by telling drivers that the car in front of them did not pay, when in fact they did, in hope the second driver will have a good heart and say, "... well, let me pay for them." She/he could be making an extra 10 bucks an hour in "tips" if this is in fact what they are doing.
But, back to the three students ... why are they saying the first car did not pay and blew through the toll and the second car paid when all of this is not true?