Wiley Mock Question 5 Duration Gap

Wiley Mock Question 5 Duration Gap talk about how the duration of assets decreases while the duration of liabilities increases. Then the duration gap is defined as:

DA - DL

Then they argue that the duration gap therefore decreases.

But I thought the duration gap was simply the difference between duration of assets and liabilities, that is here the gap should get larger (in absolute terms). Are we not using the term in absolute terms?