In this case the money they're receiving is closer to grant money than payment from a customer. But in any case, the further-up-the-thread post was just arguing that whether SpaceX will go to Mars (or anywhere else) depends in significant part on convincing their one dominant "customer", the U.S. Federal Government, to spend taxpayer money on the goal. The alternative, funding a trip to Mars entirely from private-sector funds and private-sector customers, does not appear so far to be close to materializing, considering that they haven't even successfully funded a trip to low-earth orbit via that means.
