That’s just a meaningless a phrase as “Not all men.” And “Not all white people.”
It doesn’t need to be all of them. It only needs to be enough of them to make having a horrible experience a real gamble. You have to think two or three, or even four times, about if you want to try to go there.

I have one restaurant I go to. I don’t go to any of the others. It’s been in my neighborhood for decades. There’s a bunch of them here because there’s a Little China nearby, but only just go to the one alone. I’ve been in others and a couple of stores but only when I’m in desperate need of an ingredient, and I make a point to get in and out as quickly as possible. Chinese people are NOT known anywhere for their friendliness to black people.