The comment you're replying to is shorter than my original comment where I spitballed five different hypothetical scenarios to explain why the the paper's conclusion could be true?
I think there's a solid chance it's true. I also think it's interesting that there's a discrepancy between studies like this and public perception of social media (i.e., that it's bad for kids). So I enjoy trying to feel out that discrepancy and what might be causing it.