Probably by implementing strict quarantine measures at the start of the pandemic. They likely had many undetected cases in the beginning as well, the quarantine reduced the pool of infected people a lot. Given that the number of infected people is relatively low right now, their testing capacity probably allows for fairly good tracing of cases, which is one of the primary reasons why their numbers remain low, in addition to factors such as social distancing and high hygiene standards. But the large number of undetected cases in the beginning would would reduce the ifr significantly.