It does seem like a narrow application, though 7.1% of U.S. adults is a lot of people, and sleep trouble is the first of five symptoms mentioned.
Even if it is a gotcha, Walker walked into it with his confident language claiming that "thousands of studies insist that no, there aren’t" "any biological functions that do not benefit by a good night’s sleep."
This is not the careful language that befits a scientist, certainly not a "Sleep Scientist at Google" as Walker styles himself.
Aside: In June 2018, Walker's Wikipedia entry described his work for Verily Life Sciences, an Alphabet subsidiary. In July 2018, a user named Remdreamer changed the name to "Google Life Sciences (Verily)", and changed the heading from "Verily" to "Google". Since 2015 the Verily article used the description "Verily (formerly 'Google Life Sciences')." The word "Google" does not appear on the Verily home page — nor, for that matter, can I find Walker mentioned on the team page or in the blog. Remdreamer has edited no other articles.