In situations like this, the crew is under a lot of pressure. There is a natural tendency to avoid formal declaration of an emergency and just try and get an informal traffic priority. Unless we hear the tapes ourselves, it's impossible to draw a personal judgement.
However, that said, if in doubt the controllers should query the crew directly with something like "Roger, AA 241, are you declaring an emergency?" That removes all doubt in everybody's mind.
If I had a fuel problem and I was unsure about the actual fuel state of the aircraft, I think I'd default to "emergency" and worry about the paperwork later.