That's a fair point, but I still think there's a strong correlation. To address that point specifically, users who started using Reddit early enough that the official one didn't exist, and have stuck around and are still active now, are more likely to be power users just based on account age. Additionally, many years ago those seeking out mobile apps may have been power users as well. Mobile apps are the default now, but unofficial apps have only recently been more mainstream.
Why is this the case and being repeated everywhere by everyone?
Reddit originally didn't have a mobile app and only third party clients existed. Everyone who wanted a mobile experience was using a third party app. Many of those original users never switched to the official app. How are they power users by definition?