Newspapers said relatives of the missing had been put through "heaven and hell", and accused the maritime ministry of recklessness.
Nine of the 304 people killed nearly three years ago in one of the South's worst maritime disasters have never been found.
Salvaging the wreck in one piece - finally achieved in a complex operation last week - had been a key demand of their families, who say they have been unable to mourn properly.
The maritime ministry raised their hopes Tuesday when it said that human remains had been found by workers and were "suspected to be one of the missing victims".
Little more than five hours later it withdrew the assertion, saying the pieces had been confirmed to be seven animal bone fragments.
Related reading
South Korea prosecutors seek arrest of ex-president Park
Citing forensic experts, Yonhap news agency said they were from pig legs.
In a front page headline Wednesday, the Hankook Ilbo declared: "Maritime ministry gives relatives double punch".
"Relatives of missing people had to undergo heaven and hell in one swoop as the government recklessly went ahead with an important announcement without checking basic facts," it said.
The Dong-A Ilbo daily said it had "jumped the gun", under a headline reading: "The maritime ministry goofs up, again".
Animal bones and human bones are easily discernible even to the naked eye, it added.
Relatives who have set up home at a port near the accident site burst into tears when a senior official told them "human remains" had been retrieved, the paper said.
They rushed to reach a semi-submersible anchored out at sea, where the wreck has been loaded and the bone fragments were found, only to be told of their animal origins.
Lost for words and exhausted, they returned to their shelters in silence, according to the daily.
An unidentified ministry official was quoted by the Chosun Ilbo newspaper as saying: "The bones were in muck and we were unable to take a close look at them" before forensic experts arrived. "We never imagined they could be from an animal."
Almost all the victims of the sinking were schoolchildren, and investigations concluded the disaster was largely man-made - the cumulative result of an illegal redesign of the ship, an overloaded cargo bay, inexperienced crew and a questionable relationship between the ship operators and state regulators.
The ministry was heavily criticised over the sinking, and the Kyunghyang daily said the announcement debacle happened because it was now overly eager to prove itself by producing results in the search for the missing.
Watch: More on the South Korean ferry disaster
