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.)

Each edition sold in Miami for between $120,000 and $150,000 and spurred unruly crowds: A performance artist at the exhibition ripped one off the wall, peeled the banana and ate it. Mr. Cattelan was delighted by the ensuing debate over what exactly constitutes art, and how it is valued.

By last Wednesday, those questions of five years ago seemed quaint: Bidding for Lot No. 10 — Mr. Alam’s banana affixed to a wall with a slash of silver tape — started at $800,000. Within five minutes, seven bidders drove its price above $5 million.

The artist was not compensated for the Sotheby’s sale, which was on behalf of a collector who has not been named, but he said in an email that he was nonetheless thrilled by the price it commanded.

On X, Mr. Sun crowed about his new art acquisition, and announced he now plans to eat it on Friday. He was honored, he wrote, to be the banana’s “proud owner”: “I believe this piece will inspire more thought and discussion in the future and will become a part of history.”

Nowhere in that history is Mr. Alam. (Karina Sokolovsky, a spokeswoman for Sotheby’s, confirmed that the banana was purchased from the cart where Mr. Alam works the day of the sale. The vendor himself has no specific recollection of selling an extra-special fruit.)

A widower from Dhaka, Bangladesh, Mr. Alam was a civil servant before he moved to the United States in 2007 to be closer to one of his two children, a married daughter who lives on Long Island. He said his home is a basement apartment with five other men in Parkchester, in the Bronx. For his room he pays $500 a month in rent, he said, speaking in Bengali. His fruit stand shifts are 12 hours long, four days a week; for each hour on his feet, in all weather, the owner pays him $12. His English is limited mostly to the prices and names of his wares — apples, three for $2; small pears, $1 each.

Mr. Sun, reached today via email in China, said he was moved by Mr. Alam’s response and that “his role in this artwork is not taken lightly.” He added: “His reaction highlights…. It’s a poignant remind…..unnoticed.”

He has never stepped inside the auction house. He wouldn’t be able to see the art clearly anyway: His vision is deeply impaired, he said, because he needs cataract surgery, which he has scheduled for January.

To Mr. Alam, the joke of “Comedian” feels at his expense. As a blur of people rushed by his corner a few days after the sale, shock and distress washed over him as he considered who profited — and who did not.

“Those who bought it, what kind of people are they?” he asked. “Do they not know what a banana is?”

In his email, Mr. Cattelan said he was affected by Mr. Alam’s reaction to his artwork, but stopped short of joining in his criticism. “The reaction of the banana vendor moves me deeply, underscoring how art can resonate in unexpected and profound ways,” he wrote. “However, art, by its nature, does not solve problems — if it did, it would be politics.”

For Mr. Alam, not much has changed since his banana sold. At the fruit stand, it’s still four bananas for a dollar, or 24.8 million bananas for $6.2 million.

Zachary Small and Debadrita Sur contributed reporting.