Taxi Driver Wisdom

I was in D.C. recently and it began a hot, clear trip. A couple of days into it storm clouds blew over the city and rain drops the size of Hope diamonds began to fall. I hailed a cab after dinner. “Where did this rain come from?” I asked.
“Where? You tell me where,” said the driver.
“That’s a tough question,” I said. “From the clouds, I guess. But where did the clouds come from? It looks like they come from the east–”
“No, no,” said the driver. “It’s an easy question. There are two possible answers. I know or I don’t know. It sounds to me  like you don’t know.”
We left it at that.