I believe that any situation in which a pilot needs ATC to expedite the approach due to fuel issues is called a "fuel emergency." If the pilot foresaw more ATC-related delay than he had spare fuel, I could see him declaring an emergency as the only way to bypass the delay.

In other words, it's conceivable that the pilot had more than enough fuel for normal traffic congestion levels, but not for the conditions at the time he was approaching the destination.