North Korea has accused Australian Alek Sigley of spying and spreading propaganda after releasing the student from detention.
Pyongyang's official Korean Central News Agency (KCNA) said North Korea deported the 29-year-old after he pleaded for forgiveness over his activities.
Mr Sigley arrived in Tokyo on Thursday, having earlier told reporters he was in "very good" condition, but didn't reveal what happened to him.
He had been studying at a Pyongyang university and guiding tours in the North Korean capital before disappearing from social media contact with family and friends.
KCNA said Mr Sigley was caught "red-handed" abusing his status as a student.
The agency said he was combing through Pyongyang, providing photos and other information to news sites such as NK News and other anti-Democratic People's Republic of Korea media.
NK News chief executive Chad O'Carroll dismissed claims Mr Sigley's work amounted to espionage.
"Alek Sigley's well-read columns presented an apolitical and insightful view of life in Pyongyang which we published in a bid to show vignettes of ordinary daily life in the capital to our readers," he said in a statement.
"The six articles Alek published represent the full extent of his work with us and the idea that those columns, published transparently under his name between January and April 2019, are "anti-state" in nature is a misrepresentation which we reject."
KCNA said the North expelled Mr Sigley out of "humanitarian leniency".
Mr Sigley was released by North Korea following intervention by Swedish diplomats.
After Mr Sigley's arrival in Beijing, he flew to Tokyo to reunite with his Japanese wife, who he married in Pyongyang last year.
During his time in North Korea, Mr Sigley often shared details about his life in Pyongyang through social media and the website of his travel agency, Tongil Tours.
At times, he boasted about the extraordinary freedom he had as one of the few foreign students living there.
He also wrote op-eds and essays that appeared in the Western media, including NK News, although none of them seemed outwardly critical about the North's government and political system.
North Korea has been accused in the past of detaining Westerners and using them as political pawns to gain concessions.
Mr Sigley's father Gary Sigley, a professor of Asian studies at the University of Western Australia, said his son was treated well in North Korea.
It was a much happier outcome than the case of American college student Otto Warmbier, who was convicted of attempting to steal a propaganda poster and imprisoned in North Korea.
Mr Warmbier died shortly after being sent back home to the US in a vegetative state in June 2017.
