There's a small chance this was a scam, or a distraction for some third person to come and steal things from your car. Could also have been an attempt to pass counterfeit notes to an unsuspecting person (like a tourist)
But here in New Zealand we do have a number of automated petrol stations that sell 91, 95, diesel, and perhaps a carwash. They cannot sell LPG without a qualified attendant on site, but they occasionally might have vending machines. These are also known as "truck stops"
These automated bowsers have a card reader and will pre-debit up to $150 NZD off your balance before the pump handle is raised. That's how the service station makes sure you have the wherewithall to cover the unknown total cost. If you have a credit card, that pre-charge is simply "unavailable" but you're not paying interest on it.
However if you have a debit card or an eftpos card that "reservation" can cause financial hardship.
If it was me I'd totally make a spot judgement call about the person and decide whether to help or not. If it were a spanky new car and the person had smokes then I might decide no, but a frazzled mum driving a beat-up old 90s car is unlikely to be scamming you out of some dollars. I might even hit the bowser with "dispense $20 worth" on my card rather than "fill" and then just leave without taking cash, because its nice to do something for someone.
Source - I'm a kiwi.
Further info on card charge at robo-stations: https://www.telegraph.co.uk/news/2018/05/08/petrol-stations-introduce-new-99-charge-pay-pump/ and https://gull.nz/faq/
Here's an automated fuel station. Has around 6 bowsers and sells liquid fuel only. There is nobody in attendance.
And here's the payment device at a different site. Notice that the fuel pump will not start unless the card has authorised, so if you don't have a card, or your balance is below a preset minimum, then the pump will not start.
So OP would HAVE to enter his own PIN - can't just hand over a card and share the PIN.
The reader will use the card's chip, and it may read the magstripe for confirmation but some simply ignore it. Then you MUST input your PIN. Once that validates the unit will pre-authorise $150 and signal the pump that it is allowed to start when the trigger is pressed.
So no card, no fuel. Insufficient funds and you can't even get $5 of petrol out of these things.
If its a scam, its a lot of work for a little bit of fuel.