The unprecedented growth spurt was far in excess of anything seen before, and sparked both mystery and concern as people wondered how the astronaut had stretched out so much.
But Mr Kanai has now confirmed that the measurement was a mistake. He had only grown by a couple of centimetres, he confirmed, after checking again in response to shock at how long he had become.
He headed into space last month for a nearly six-month mission on the floating lab. On Monday, he posted that he had a "big announcement".
"My height's been measured here in space and somehow, somehow, I've grown 9 cm! In only three weeks I've really shot up, something I haven't seen since high school," he tweeted.
"This makes me a little worried that I might not be able to fit in the Soyuz seats for our return."
But just over a day later – as international news stories voiced concern and interest in the strange phenomenon – Mr Kanai apologised. His captain had raised questions about his measurements and he did them over again – and they showed that he had only grown 2cm, in line with normal expectations.
"This mis-measurement appears to have become a big deal, so I must apologise for this terrible fake news," he tweeted, without explaining how the original miscalculation had occurred.
"It appears I can fit on the Soyuz, so I'm relieved."
Astronauts usually stretch out as they get to the space station, as the reduction in gravity allows their spines to unspurl a little and can add a couple of centimetres. But Mr Kanai's reported growth was unheard of, leading to mystery about how exactly he could have stretched out so much.
Read the original article on the Independent.
More about: #astronauts