Seat utilization is a big factor here, but let's take the worst case for a car vs. the best case for a helicopter.

Assume that the helicopter can make 3 trips per hour (8 minutes flight time, plus 12 minutes turnover).

950 / 3 = 316 lbs of C02 per flight. It looks like the Bell 430 configuration they have has 6 passenger seats, so 52.7 lbs of C02 per passenger.

Even if the taxi has only one passenger and takes 1.5 hours to reach JFK in moderate traffic, that rider will only be generating 33 lbs of C02 (37% less C02 than a helicopter in a best-case scenario for the helicopter).

Buses do produce more CO2 than cars, but are generally 6-8 times more efficient on a passenger-mile basis.

I'm more confused how a helicopter that's 2500 lbs empty can somehow spit out over 900 lbs of emissions every hour for its four hour flight endurance. They've got to be doing some tricky calculations to get there. I'm guessing it looks more like consideration of infrastructure and production than it does passenger-time.

Why is time relevant here? I'd have thought it would be better to compare the CO2 emitted by one heli trip to the airport from central NYC to the CO2 emitted by one taxi trip to the airport from central NYC, in both cases divided by the number of passengers.