Jose Salvador Alvarenga, 37, declared he owed his survival to his faith in God.
He appeared strong and walked unaided from the hospital but he also appeared to be disoriented and had trouble speaking.
Mr Alvarenga, a Salvadorian, said he did not plan to tell his story and did not want to remember the ordeal.
“I always had faith that I was going to survive, asking [God] every day and every night,” he said. “I never lost faith that one day I would be found.”
Asked about the fate of his fishing companion, Ezequiel Cordova, 22, Mr Alvarenga said Mr Cordova lived four months in the boat before succumbing to starvation and exposure.
Mr Alvarenga has said that he lived on fish, turtles and birds and that Mr Cordova had difficulty eating raw food.
Reporters asked if Mr Alvarenga had eaten Mr Cordova to survive, and he answered with an emphatic: “No.”
“He died of starvation and the sun,” Mr Alvarenga added.
He said Mr Cordova’s parents should not worry for their son because he died praying to God: “The whole time he was asking for forgiveness.”
Mr Alvarenga’s story drew global attention when he washed up on a Pacific atoll several weeks ago, seemingly robust and barely sunburned. But he turned out to be swollen, dehydrated and in pain from his ordeal.
He has said he came close to giving up hope of being rescued after several large ships came near his small fishing boat but none tried to rescue him, even though sailors on at least one even waved at him.
Doctors have been amazed by his physical condition after travelling 6,500 miles in a small fishing boat from Mexico to the Marshall Islands. He was believed lost in a storm while fishing off the coast of Mexico.
As he was released from hospital, doctors said he seemed mentally well, though he is afraid of returning to the sea.
“He doesn’t exhibit grave mental disorders like we feared, such as problems with thinking or perceptions,” said psychiatrist Dr Fredy Sermeno.
Mr Alvarenga underwent a range of tests at the hospital after being flown home.
The medical team that examined him at San Rafael Hospital in El Salvador’s capital said he was in remarkably good physical health, with no skin lesions from overexposure to the sun and no cardiovascular or kidney issues. His only physical problem was anaemia, doctors said.
Salvadorian experts who looked at Mr Alvarenga’s results said they did not doubt the veracity of his tale, which left many people sceptical even without any alternate explanation for his appearance on the Ebon atoll.
Mr Alvarenga said he was working in a fishing village on the Pacific coast of Mexico’s southern Chiapas state, from where the boat sailed.
A man with his nickname, “Cirilo,” had been registered as missing with civil defence officials in the village.
The officials said a small fishing boat carrying two men, the other named Ezequiel Cordova, disappeared during bad weather on 17 November 2012, and no trace of them or the craft was found during an intense two-week search.
Mr Alvarenga asked to be given as much privacy as possible amid an international media storm over his story. He plans to return to his home town of Garita Palmera for a brief visit.