Good point, didn't quite get the right. Here's a better/clearer (I hope) explanation. (Maybe I'll update the doc with this as well if it makes more sense to you.)

Mars produces propellant dirt cheap locally.
To export it:

• Fill tanker on Mars with ~1 200 t propellant
• Launch full from Mars – still only needs roughly twice the propellant of an empty launch because of low gravity (total ~300-400 t expended to get ~1 200 t payload to orbit/escape)
• Net: deliver ~800-1 000 t pure propellant profit to LEO
• Sell it there at market rates ($500-$2 000/kg)

Mars becomes the low-cost producer and exporter of fuel to the entire Earth-moon system.

The return trip is empty (or carrying high-value small cargo back), aerobrakes, lands with almost no fuel used, refills on Mars, repeat.

No need for Earth to send fuel out – Mars sends fuel in.