At a moderate downhill left-hand curve, he skidded off the road.
When he attempted to correct the mistake, he lost control, swung across the road, and hit a bank.
The campervan tipped onto its passenger side and came to rest.
His friend, compatriot, and front-seat passenger Yi-Chieh Feng, 30, was killed in the crash.
At Christchurch District Court this afternoon, Chen admitted a charge of careless driving causing death.
Ms Feng's parents and sister flew to New Zealand after the smash.
In court today, her sister said the family were "very saddened" by the tragedy but they still felt sorry for Chen.
The family has been staying at the same Christchurch hotel as Chen ahead of today's court appearance, and they feel he is "sincere and remorseful".
Through an interpreter, the grieving sister said they "understand how he feels and hopes the court will not penalise him severely".
Defence counsel Grant Tyrrell said the facts of the case were "painfully clear", with Chen's "momentary lapse" resulting in tragedy.
The lawyer said the case reinforces the importance of wearing a seatbelt.
But he also stressed that mistakes on the road are not just the domain of tourist drivers.
"Anyone can make a mistake. I just hope this is a reminder to all drivers on our roads that great care is required, particularly in winter conditions," Mr Tyrrell said.
Chen, a highly respected senior Taekwondo instructor, was a person of good character, Mr Tyrrell said.
It was a tragic case, he said, which showed "you don't have to be a bad person to make a mistake with terrible consequences".
Chen and the Feng family plan to fly home on Monday.
Mr Tyrrell said Chen, who was not injured in the smash, has paid Jucy Rentals' $5000 insurance excess and also made a commitment to assist the family on their return.
Judge Brian Callaghan said the Feng family have shown a "remarkable sense of forgiveness" towards Chen.
"Nobody holds a deep grudge against you which I could understand they might well do," the judge said.
Chen and the Feng family will "always have this hanging over them", he added.
Judge Callaghan ordered that Feng pay $3500 in emotional harm reparation to Feng family "just as a further token of your remorse". He also disqualified him from driving for two years.