Not a 90% chance that it was a scam.
99.999% chance. He was probably scoring drugs. Lots of successful people (financially speaking) have drug habits to support.
The best thing to do (Monday morning quarterbacking, I know) is to offer to walk into the store and pay for the medicine for him.
One time a man approached me at a gas station with the same old story:
"on my way to Texas, don't have enough money, lost my debit card, called the bank and they said the nearest location is Texarkana, AR ... please spot me $5 for gas." I wasn't about to offer to go in the store with him to purchase the gas, as my wife and child were in the car and I would leave them without protection if I went inside. Grudingly handed him a five, got in my car, and drove off. As I recounted the story to my wife she reminded me that it was a federal holiday,
and the banks were closed. Damn.
As I age (and become slightly wiser, though still stupid in the grand scheme of things) I get better at being "rude" to these people, and forcing them to let me pay for the gas or telling them "stand further away from me" as I reach for my money clip. It's just prudent.