Maybe he's saying that he drove himself for $3 in gas (while conveniently ignoring all the other costs of car ownership, not to mention the massive externalities).
It's reasonable that if GP needs and already has a car for other non-commuting purposes (shopping, road trips, etc.) the choice in their specific case is between paying for public transit and only paying for gas to cover the commute.
Cost of insurance and wear & tear are direct costs of each trip outside gas, not including those (which is ~50% of the cost of each trip) is deceiving yourself.