That is the value with something close to capacity, but most importantly assuming worse case for weight. And weight has a bigger effect on the consumption on a plane than on a car. So if your plane has less passengers, the MPG of the plane increases, though the MPG/passenger decreases. And it is also mainly for cruise - the longer the travel, the better the efficiency. Taking off and climbing is not that efficient so short haul trip are quite bad.

To me the point is that an airplane MPG/passenger is of the same magnitude as the MPG/passenger for an individual car. What is bad is not necessarily the plane itself, but the fact we do very long distance trips. Trains and buses can be more efficient, carbone-wise, but requires a traffic big enough to offset the carbone cost of the infrastructure needed.