Not to be rude, but this is incorrect.

"Books" also include assets and liabilities, and assets an liabilities are neither income nor expenses. And balancing the books has nothing to do with ensuring income is equal to or exceeds expenses.

As others have said or implied, I really doubt that average browsing time is a good analog for average attention span.

As others have alluded to, it doesn't distinguish between looking at a website to see if it's what your looking for, realizing it's not, and then leaving; as opposed to finding that it is what your looking for. Even if it did, I really doubt that the amount someone spends on a single website reflects their attention span.

And on the source, the use of footnotes is kind of weird. For some claims, there's a footnote with citation, but for a good number of claims there's nothing. For example, it mentions that "Microsoft found..." and lists of a bunch of numbers, but no citation.