The data is interesting, but I am always skeptical of self-reported sleep times. It seems there is a sense of pride some people take in sleeping less than others.

There's definitely reason to be suspect, although it looks like, on the average, it might be the reverse of what you seem to be expecting (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2785092/):

"Our model suggests that persons sleeping 5 and 7 hours over-reported, on average, by 1.3 and 0.3 hours respectively."

For self-reporting sleep studies, perhaps people have it in their head that 8 hours is how much they're "supposed" to sleep and they over-report to better match that?

Of note, however, while the CDC data I linked comes from the Behavioral Risk Factor Surveillance System which does appear to be merely a self-reporting survey question (https://www.cdc.gov/sleep/surveillance.html), the data in the Economist article comes from an app (www.sleepcycle.com). Granted, I suspect the latter almost surely suffers from some kind of non-trivial selection bias.

Would be interesting to look at smart watch data to see actual averages. You can tell when a person is sleeping by watching their motion activity (obviously) in combination with a drop in heart rate.