Ōmokoroa fire chief Ian Blunt said on Thursday the fire appeared to have started in a double garage and spread to the family home.
A fire investigator was called to the scene to establish the cause, he said.
Lett told the Bay of Plenty Times he was "grateful" that nobody was hurt. The tenants, a mother and daughter, were both away at the time, with the mother at work and the daughter at school.
They did not want to speak to anyone, Lett said, as they were "pretty upset".
"They've lost everything," he said, and they are staying with family in the area until the insurance payment comes through and they can find another flat.
The community had rallied around both the Letts and their tenants, he said.
"Our phones have just not stopped [ringing] with offers of help," Lett said.
"There were about 50 people turned up - the Te Puna and Ōmōkoroa communities are absolutely amazing."
He'd had "about 100" phone calls within half an hour of people hearing about the blaze, he said.
"Facebook's been going mental - not that we need it, it's not our house as such ... there's been a lot of help offered to the tenant, which is outstanding."
Lett also wanted to thank the Ōmōkoroa, Greerton, and Tauranga crews who fought the blaze.
While the cause of the fire was still under investigation, Lett did not believe the cause was deliberate.
"The orchard manager went spraying and then came back and it was on fire."
Lett said he wasn't going to rebuild the property as a residence but would rebuild the warehouse next door, because the property sat next to a kiwifruit orchard.
"You just get on with your life and sort all the mess out," he said.
Fire and Emergency NZ were contacted but were unable to comment in time for publication.