Yes, that's pretty close in at least one sense, though not for the entire trip.
As noted here
The Saturn V rocket’s first stage carries 203,400 gallons (770,000 liters) of kerosene fuel and 318,000 gallons (1.2 million liters) of liquid oxygen needed for combustion. At liftoff, the stage’s five F-1 rocket engines ignite and produce 7.5 million pounds of thrust.
At an altitude of 42 miles (67 kilometers), the F-1 engines shut down.
The "mileage" of the first stage can be calculated from that information as 42 miles/203,400 gallons of kerosene, which works out to 0.000206 miles/gallon, or 13 inches per gallon of kerosene. If both the kerosene and oxygen are included, the answer is 42/(203,400 + 318,000) = 0.00008 miles/gallon, or 5.1 inches per gallon.
Buzz's value of 7 inches per gallon is accurate during the first stage portion of the flight.
Conversely, if you factor in the entire trip, their fuel economy (counting oxidizer) is pretty close to 1 mile per gallon. 947,529 gallons and about 953,700 miles (828,743 nautical miles)