No, there are two criteria: pressure and weight. The first is measured with a pressure gauge. The second requires a scale...
Now how it could be in compliance with one and not the other is a different issue.
Buy a football.... air it up. Weigh it. Soak it in water and then let the air out. It will weigh more than it did before you let the air out.
The intent here is to negate the possibility of a team inflating the game balls with Nitrogen as opposed to compressed air (~20% Oxygen).
If the home team inflates every ball used in practice with nitrogen, they have an advantage; the balls will be slightly heavier; likely above the 13.5 Oz prescribed.