If you go back to the first slide, it explains the methodology. To my reading, they didn't survey 4473's (wouldn't that be a federal registration? Didn't the BATFE just get busted for keeping 4473's past the regulation date...by like 20 years?). They didn't conduct a public survey. They know how gun owners will respond to, "Hi, this is CBS news. How many guns do you own?" They would have reported about 100 guns nation wide! lol
The slide indicated they only surveyed NFA data.