Founded by conservative commentator Dave Pellowe, Axiomatic Events organised a series of speaking engagements for far-right YouTubers Ms Southern and Stefan Molyneux in Australia in July last year.
The Guardian reports that the boat trip was organised so Ms Southern, a Canadian woman who arrived in Australia wearing a "It's okay to be white" T-shirt and has handed out pamphlets declaring "Allah is gay", could meet Mr Christensen, a controversial marine scientist and some young conservatives.
On Friday, Mr Pellowe tweeted that the trip was organised so Ms Southern could do a documentary on the reef condition, not so she could meet Mr Christensen.
"Evidence: they'd ALREADY met prior to the boat trip," he tweeted.
He said Ms Southern decided not to go ahead with filming a documentary "due to miscommunication".
Mr Pellowe also disputed descriptions of Ms Southern as "far-right", arguing his family had been "harassed" for not being far-right.
Mr Christensen claimed $1612 in expenses for two nights of accommodation and flights for the July trip which he listed as part of his parliamentary duties.
While the documentary did not go ahead, Mr Christensen posted a Facebook video of a discussion with controversial reef scientist Professor Peter Ridd on the boat.
"As a scientist, Peter reckons the reef is brilliant. Not dead or dying," Mr Christensen posted.
Mr Christensen's office and Ms Southern did not respond to requests for comment.
Buffalo horns, flowers and Foxtel for every MP
The latest declarations of financial interests reveals the generous and unusual gifts Australia's federal politicians have received from their constituents and companies.
Among the most unusual items, new Liberal MP Gladys Liu declared an ornament given to her by a feng shui master of unknown value.
While only gifts valued at more than $750 need to be declared, some MPs have opted for maximum transparency, such as Labor MP Jason Clare who declared a $40 bunch of flowers from the Grand Mufti and a book on refugee rights.
More quirky presents include a set of buffalo horns given to Northern Territory MP Luke Gosling, a stamp set from Australia Post for Brisbane MP Trevor Evans and a bathroom tap given to MP Graham Perrett.
The most common perks were tickets to AFL and rugby league matches, some worth several hundreds of dollars, and concerts and festivals.
New Independent MP Zali Steggall attended last month's four-day Splendour in the Grass festival as a guest and she participated in a panel of politicians at the festival.
The former winter Olympian also enjoys an annual lift pass to Perisher snow fields.
Labor MPs Joel Fitzgibbon and Matt Keogh were among those to benefit from the generosity of mining companies.
Mr Keogh received box tickets to the State of Origin game in Perth in June thanks to Mineral Resources and was flown by Fortescue Metals Group to the site of a new mine near Tom Price in Western Australia for a sod turning.
Mr Fitzgibbon, who had pushed Labor to take a stronger pro-mining stance, received two tickets and hospitality at a Knights NRL game in April from NSW Mining.
All MPs receive membership to airline lounges and Foxtel provided to their offices.
Despite holding the top job, Prime Minister Scott Morrison declared no gifts, only flight and hotel upgrades for him and his family for a recent trip to Fiji.
This article was amended on 7 August, 2019 to make clear that Ms Southern did participate in the trip, but did not interview George Christensen.