Mr Wichman denied the claim, saying it was another staff member who assaulted Mr Kereopa.
A few months later in April, a piano fell on Mr Kereopa's foot at work and he said he could no longer drive the truck because of the injury. He took three weeks off work to recover. On April 26 last year his boss told him, "f*** you, you're fired", Mr Kereopa told the hearing.
Mr Wichman later threatened to go to Mr Kereopa's house to "smash" him, Mr Kereopa alleged.
He complained to the police and had a trespass notice issued against his former boss.
Mr Wichman denied the allegations, saying Mr Kereopa abandoned his job and his pay was being withheld as a result.
He did admit however, he "lost my temper with him and told him I'd like to beat the sh** out of him", said the finding.
Mr Kereopa told the authority he was very upset over losing his job.
"I was just really gutted ... felt small and useless and as if I couldn't provide for my kids and embarrassed.
He continued to have chest pains from the alleged Christmas party incident, he told APNZ.
The ERA decision was "justice to everyone who's been done an injustice", said Mr Kereopa.
Mr Wichman did not attend the hearing and gave no reason for his absence, but did provide a statement of evidence prior to the hearing.
ERA member Christine Hickey found Mr Wichman dismissed Mr Kereopa, and did not follow fair process when he did so, making the dismissal unjustified.
"Mr Wichman's actions were certainly more than inconsiderate conduct. Even in the context of a fairly robust workplace his actions were dismissive and repudiatory. His actions were very far from the standard of a fair and reasonable employer. Mr Kereopa's dismissal was unjustified," she said.
Mr Wichman could not be reached for comment today.