Speaking from Australia, Mr Callaghan said he had been briefed by Crown solicitors last week on the reasons the charge could no longer be pursued.
"I understand that; you've got to have evidence,'' he said.
"At the end of the day it's not going to bring Chelsea home.''
Mr Callaghan said he had never heard from Mr Kukutai or anyone from Riverland Adventures.
"The thing that surprised me was that while all this was going on he was still able to operate,'' he said.
"Obviously the authorities didn't think it was necessary to shut him down.''
Ms Callaghan is buried in Victoria with her parents, who both died of cancer. Her father passed away, aged 68, one year to the day before Ms Callaghan died.
"It was very sad,'' Mr Callaghan said. "I couldn't believe it when I got the phone call to say that she was on life support.''
Mr Kukutai was charged with manslaughter in April, but was discharged at an appearance in the High Court in Auckland on Wednesday.
Justice Timothy Brewer told Mr Kukutai that the case had been reviewed by the Crown Solicitor and the Solicitor General, who had agreed there was insufficient evidence of negligence.
Justice Brewer said the degree of negligence necessary to find a criminal charge was very high. "It goes well beyond mere carelessness,'' he said.
Riverland Adventures also faces charges brought by the Ministry of Business, Innovation and Employment in relation to breaches under section 16 of the Health and Safety in Employment Act.
A hearing will be held next month at Manukau District Court.
Mr Kukutai could not be reached for comment.
