The old "he needed gas to get home" story.
Unless I was actually looking at him standing in front of his car I would assume he was panhandling. Most men keep their drivers license in their wallet which also hold their credit cards.
Secondly most cars have gas gage and an "older gentleman" is far more likely to (know) how much gas he has in his car at any given time. If you know how far you're driving the first thing you'd do is check to see if you have enough gas to make there and back home. That's commonsense.
"Note: he did not ask for your help, you notice the desperation in his voice on the phone and his demeanor." This is called "dry begging".
Essentially you tell a person about your hardships and let (them) volunteer to help you out. Even family and friends are sometimes guilty of this. If you ever call them on it the first thing they will say is:
"I never (asked) you for any money or help!"
If the older gentleman had access to a Triple A card or road service card he could have had his car towed back home or he could have had a taxi take him home to get money/credit card or to a family member/friend who could help him out. It's also possible he could have taken a taxi to his bank and they could have pulled up his account using his driver's license after explaining the emergency to the branch manager.
Something tells me if you showed up with (a gallon of gas) instead of money the "older gentleman" would have been disappointed!
Don't get me wrong, I have given money to strangers on the street before but not if I believe it's a scam. Generally the mood I'm in and the amount of cash I have on me determines whether I'd spare a $.