NYC Taxi Cab Scam--did he just want cash or did his machine just not work?

I was in NYC last weekend and took a cab to LGA Sunday morning. I was running a little late and the cabbie noted that I should not use GPS as there were road closures for a race. It did seem like there were road closures up the east side of Manhattan and I did see a half marathon on google. I was staying south of 14th street, but the driver drove me north up the west side highway and around Manhattan--often speeding along a what seemed like light speed. We did arrive at the terminal but every one of my credit cards was declined in his machine. He tried to get me to Venmo him money but I said I didn't have it. The fare was around 70 dollars and I only had twenty some dollars in my wallet. I said I would have have to go to an ATM if he couldn't run my credit card manually through one of those embosser things. He said no. I don't use cash a lot but I did find a random 50 I had in my luggage from a trip abroad a few years ago. Basically I was looking through my carry on one curb for cash. I was able to round up enough for just the fare but no tip. He seemed fine with that and sped away. I'll have to remember to carry more cash before traveling. next time. My credit card worked just fine in the terminal to get lunch. I'm still perplexed.....