I'm also suspicious on principle of statistics which suggest but don't actually show what they're trying to measure. If nearly half of young adults have really stopped using Facebook, surely there's a more direct statistic showing it.
Now, we don't know how big of an effect perceived popularity has on other self-reports of past actions, but we have plenty of reason to believe it plays a significant role.
People, the concept of "revealed preferences" (https://en.wikipedia.org/wiki/Revealed_preference) is highly relevant here. What people say in surveys is often garbage, for all kinds of reasons, social desirability bias among them. This article is useless compared to actual measurements of people's phone and time.
It also tells them that the App apparently dosn't give value to users and something has to change on their side (whatever "something" might be, might be reputation or features or overall experience or ...)