Scott Brown, named as Washington's man in Wellington and envoy to Samoa in one of US President Donald Trump's earliest diplomatic appointments, confirmed the probe followed comments made at a Peace Corps event in Samoa in July.
The 58-year-old told New Zealand journalists this week he had called guests "beautiful" and suggested to one waitress she could "make hundreds of dollars" working in the service industry in the United States.
While Mr Brown acknowledged there may have been cultural misunderstandings, he also believed there was an element of "political motivation" behind the complaint.
"At this event there were a lot of people that didn't like [President Trump]. Sadly it's politics and it is what it is," he said.
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Mr Brown said he was revealing what happened because of mounting "innuendo and rumour" about a State Department investigation into his behaviour.
He said an official complaint had been made about his remarks and an "administrative inquiry" concluded he should be more culturally aware.
Mr Brown commented on the appearance of guests because when he and his wife, Gail, saw people before the event "they were all like dirty and grungy ... We walked in and everyone was dressed to the nines," he said.
"They all looked great, Gail looked great, you know I was dressed up and Gail and I both walked in and said 'you guys are beautiful, you look really handsome sir, you guys are great'. And apparently somebody took offence to that," Mr Brown said.
He also told some staff they would do well working in the United States.
"Absolutely, told people they could make great waitresses," Mr Brown said.
"And as a result of that I was told that, 'you know, listen you're not Scott Brown from Ryan, New Hampshire anymore, you're an ambassador and you have to be culturally aware of different cultures, and different sensitivities' and I'm always welcoming that kind of advice."
Mr Brown, an attorney and long-time triathlete, has had a varied life.
He was once named "America's sexiest man", working as a male model, serving as the Republican senator from Massachusetts, and rising to the rank of colonel in the Army National Guard.
