However, he later moved to clarify his position on climate change.
"I do not want people to think that criminal behaviour, while reprehensible, is the main reason for the devastation this bushfire season," he said in a statement, issued to SBS News.
"If my statements earlier this morning were not clear I would like to say, unequivocally, in my view climate change is real. I accept that the warming of our planet is a primary cause of the catastrophic events we have been experiencing.
"Arson may be responsible for starting fires in some cases, but it is not the reason the fires have reached the proportions they have through this season and it is not the reason they have continued for so long."
Experts have discredited the theory arsonists are to blame for most of this summer's horror fires.
On Wednesday, Mr Forrest pledged $70 million to the bushfire recovery effort through his philanthropic Minderoo Foundation.
He specified $10 million would be used to mobilise at least 1,250 specialist volunteers from Western Australia to assist firefighting and recovery efforts in Queensland, Victoria, New South Wales and South Australia.
WA mining billionaire Andrew "Twiggy" Forrest will spend $70 million on a bushfire recovery package
'We weep along with Australia'
"We're stepping up as we did for the Black Saturday Bushfires [in Victoria in 2009 which killed 173 people] to support the communities in South Australia, Victoria and New South Wales. [We're stepping up to] find out what you need, what your families need, what your communities need and to help you plan what may be even better [than what you had]," Mr Forrest said.
"And I'd just like to say - on behalf of the Mindaroo Foundation - that we weep along with Australia, along with you. And as a family and as a foundation we would like to step up and help you."
Another $10 million will fund immediate relief work, while the bulk of the money will be invested in the development of a long-term blueprint for fire resilience.
Former CSIRO data boss Adrian Turner has been appointed to lead the project which would consider the aspects of mental health, water security and climate change.
Mr Forrest's pledge dwarfs the contributions from a host of celebrities such as reality TV star Kylie Jenner and actor Chris Hemsworth who have donated $1 million each.
Veracity of social media campaign rejected by police
Experts have discredited the theory of arsonists being the key factor to blame for the intensity of this bushfire season.
Victoria Police said arson is incorrectly being identified on social media as the chief cause behind the fires burning in the state.
"Police are aware of a number of posts circulating in relation to the current bushfire situation, however currently there is no intelligence to indicate that the fires in East Gippsland and north-east Victoria have been caused by arson or any other suspicious behaviour," a Victoria Police spokesperson said.
The hashtag #ArsonEmergency has sprung up on Twitter in the past week, seeking to capitalise on the popular #BushfireEmergency hashtag by propagating the theory of arsonists being to blame for the bushfires, downplaying the role of climate change.
A Queensland University of Technology Analysis examined 1,500 tweets using the hashtag #ArsonEmergency to find that many of the accounts appeared to be bots.
Comedian Celeste Barber's fundraising efforts have raised more than $47 million.
Australian actor Nicole Kidman and US singer Pink have also said they will give $500,000 to fire services.
Another philanthropic organisation, the Paul Ramsay Foundation, has donated $3 million to charities working on the bushfire response, as well as $27 million for long-term rebuilding efforts.
Australia's richest woman Gina Rinehart responded to questions about her apparent lack of contribution from Barber, saying she made a private donation to a firefighting fund on Tuesday.
"Where the hell are you and all your money?!" Ms Barber tweeted on Tuesday.
Ms Rinehard did not detail the sum donated.
In a statement, a spokesperson for the mining billionaire urged "red tape" issues be addressed, such as restrictions on building dams, and land clearing which she said had helped cause the loss of life, property damage and much suffering.
"[Ms Rinehart] is most concerned that the true causes of this sad devastation are tackled, rather than missed in the rush to blame climate change," a spokesperson for Ms Rinehart said.