Mr Gambo wanted to make further inquiries with immigration authorities in Australia.
In that same conversation with Mr Yan, Mr Gambo alleged that Mr Yan admitted he used two identities because he didn't want Australian immigration officials to "know that I've been there".
The Crown said that evidence showed dishonest intent and therefore Justice Brewer could infer Mr Yan did the same with New Zealand authorities.
Justice Brewer said the Crown submission was speculative and he was not sure the "admission" was made in the words and context reported by Mr Gambo.
"My impression of Mr Gambo is that he is a dedicated and competent public servant. He is a strong guardian of the immigration processes.
"He certainly did not like the way, as he saw it, those processes were being overridden in the accused's case. I emphasise that I find him credible. I am not sure of the reliability of his account, however," Justice Brewer said regarding the so-called Australian visa admission.
In other parts of his evidence, Mr Gambo said he was "told to just process the file, send it to Wellington, don't worry about asking any more questions. "I have been working there for seven years and that was the first time I have had my boss phone me about an application."
Asked who called him, Mr Gambo named the general manager of citizenship, Geoff May.
Mr Gambo said he told Mr Yan at a meeting in May 2008 that it was unlikely he would get citizenship because there were so many unresolved issues.
"He said to me, 'I'm confident it will be okay. I've got a lot of support from the MPs'."
Former Labour MP Dover Samuels, a friend of Mr Yan, wrote several letters in support of his citizenship bid and was in court.
While Mr Yan was acquitted of the immigration fraud charges, questions remain over why Labour MP Shane Jones granted him citizenship against official advice when he was a Cabinet Minister.
Mr Jones granted Mr Yan citizenship in 2008 against the advice of officials, who said there were questions about whether he met good-character requirements because he had two passports with two names and two birth dates, and was wanted in China for an alleged large-scale fraud.
Labour leader David Shearer has stood down Mr Jones from the front bench but said the MP would be reinstated if the Auditor-General found he acted properly.