At the fruit stand where he works on Manhattan’s Upper East Side, Shah Alam sells dozens of bananas a day at 35 cents a piece, or four for a dollar. He does a brisk business in cheap fruit outside Sotheby’s auction house; inside, art can sell for millions.

But last Wednesday, Mr. Alam sold a banana that a short time later would be auctioned as part of a work of absurdist art, won by a cryptocurrency entrepreneur for $5.2 million plus more than $1 million in auction-house fees.

A few days after the sale, as Mr. Alam stood in the rain on York Avenue and East 72nd Street, snapping bananas free of their bunches, he learned from a reporter what had become of the fruit: It had been duct-taped to a wall as part of a work by the Italian artist Maurizio Cattelan, and sold to Justin Sun, the Chinese founder of a cryptocurrency platform.

And when he was told the sale price, he began to cry.

“I am a poor man,” Mr. Alam, 74, said, his voice breaking. “I have never had this kind of money; I have never seen this kind of money.”

The banana’s journey from fruit stand to artwork began in 2019, when Mr. Cattelan first exhibited the work at Art Basel Miami Beach, the international art fair. The conceptual piece of three editions, titled “Comedian,” is an implicit sendup of the absurdity of the art world, in keeping with Mr. Cattelan’s puckish oeuvre. It came with a detailed owner’s manual on just how to affix the banana with the tape, and permission to refresh it when it rots. (Mr. Cattelan bought the original bananas at a Miami grocery store, he has said in interviews.)