I don't believe the title implies that his primary concern is explaining an intelligence increase.

There are two ways of looking at the interaction between pop culture and intelligence. You can start by analyzing intelligence and noticing that it seems to increase, and then trying to figure out why, and then figuring out that pop culture caused it. Or, you can start by analyzing pop culture, and then noticing that it seems to do things that would have cognitive benefits, and then attaching this to the increase in intelligence as a factor that helps explain it. The book does the latter, not the former.