Video games boost skills, but can also be harmful

For me, the most interesting part of the article is this. On the part where it is claimed that gaming may improve cognitive skills, they put in this disclaimer:

The researchers said the study doesn’t necessarily prove whether playing video games improves learning ability or whether people with an innate ability become gamers because they find gaming more rewarding.

Which is fair enough, but an equivalent one is not put in for the one that claims that playing too much video games is related to hyperactivity, thus implying that the only conclusion is that video games cause hyperactivity.

I wonder what is the cause of this difference.