In April, the New York Times and German broadcaster ARD reported that the swimmers had tested positive for trimetazidine (TMZ) at a domestic competition in late 2020 and early 2021.
It was determined by Chinese anti-doping authorities they ingested the substance unwittingly from tainted food at their hotel and no action against them was warranted.
The World Anti-Doping Agency (WADA) accepted the argument of the Chinese authorities and did not sanction the swimmers, 11 of whom have been selected for the Paris Olympics which start this month.
The case caused a global uproar, with US anti-doping authorities accusing WADA of a cover-up.
As a result, WADA set up an independent investigation overseen by retired Swiss prosecutor Eric Cottier, whose interim findings were released on Tuesday.
"There is nothing in the file -- which is complete -- to suggest that WADA showed favouritism or deference, or in any way favoured the 23 swimmers who tested positive for TMZ," the report said.
WADA president Witold Banka was in fighting form after the executive board had met and endorsed the report.
Banka told AFP that WADA had been caught in the middle of a tug of war between China and the United States.
"This case was used as a geopolitical tool," he said.
Banka said it was not new for WADA or him to be targeted in such a manner.
Recently the head of Russian intelligence had accused him of trying to "destroy Russian sport" after he criticised the Moscow-organised Friendship Games.
He also received death threats when WADA appealed the doping case against China's swimming superstar Sun Yang in 2021.
WADA's fiercest critic has been Travis Tygart, head of the US Anti-Doping Agency (USADA), who has claimed there was a cover-up and that the body needed reforming.
Banka, 39, said there had been "disgusting allegations about a cover-up by some individuals in the US."
The former Polish sports minister said "all the statements are under the analysis of our external legal experts."
"I am very sad that people tried to accuse us of really terrible things," said Banka, who has been in his post since January 2020.
"If this case had happened in another country than China, it would not have brought attention."'Dangerous situation'
Banka claimed USADA were effectively trying to usurp the global anti-doping body.
"What is happening in the US is a very dangerous situation for the future of doping," he said.
"One country wants to investigate and analyse cases in other countries, even in national competitions.
"So what is this, actually?"
The US Department of Investigation is probing WADA's handling of the case and has summoned the executive director of World Aquatics (WA), Brent Nowicki, to testify in the case.
One of the 11 Chinese swimmers set to appear at the Paris Olympics is reigning men's 200 metres medley champion Wang Shun.
That event will feature France's strong gold medal hope Leon Marchand.
When it was put to Banka that the home crowd might react angrily if Marchand lost to his Chinese rival, he said it would be an "unfair" reaction.
"Coming back to the outcomes of the investigation, there is no evidence that they were guilty, so it is unfair (to accuse anyone)," he said.
"Until you have evidence to challenge it, you cannot accuse people of doping.
"Legally there is no evidence to challenge the contamination theory."
The contamination defence has in the past often failed to be sufficient in individual doping cases.
However, Banka said this case of mass contamination would prompt a wider debate.
"We have to have a serious discussion about contamination cases, because I see more and more contamination cases, especially in the US, I have to say."
