Earlier quoted context omitted.
Just guessing what he meant: The black cars in NYC with an iPhone on the dashboard running the Uber app aren't necessarily getting 100% of their fairs via Uber. If they see you as a potential client, they'll still try to pick you up off-network. If you already hailed an Uber, an unscrupulous driver may potentially tell you "Yeah, I'm from Uber". Although I'm not sure how they'd convince you to pay cash.
I was at W NY finishing my talk for HOPE X with my cospeaker; we were speaking at 2300h Friday so we took an Uber Black from the W to the Hotel Penn around 2100h. An Uber came within 2min of us calling it, approximately the right time, and we were a bit distracted. Walked over to the town car displaying the U logo, and I don't recall exactly, but somehow "You're Marc, right?" got exchanged, and we got in. The driver…
I am not sure the word gentleman means what you think it means ;)