That's not the average cost per person; it's simply the total amount of health care spending, in all categories, in the US divided by its population.

Which is also the arithmetic mean cost per person, by definition. Which average did you have in mind?

The median might arguably be a more useful average here, but I doubt the data necessary to even identify the median individual cost are kept.

The person you responded to was talking about direct-to-consumer costs; you switched figures while suggesting that their number was erroneously low. You were wrong.