They had just finished research projects for their iwi Ngāti Kahu, interviewing kaumatua and kuia about their lives.
"In all their interviews we could hear the hurt and the mamae, and that's what drove us to just action it, to do what we did that day," he said.
When the pair were sentenced for the assault, they apologised to Key and to people "the length and breadth of New Zealand".
"But when will we get an apology for the illegal confiscation of our harbours, of the land taken from us?" Popata asked in court.
Just a few years later, in 2011, he was back before the court on two more assault charges, school boys who had been witnesses to a drunken Auckland robbery carried out by his cousins.
For that he was sentenced to six months' home detention.
At that point, his life could have gone either way.
"Then I met my partner and we had our first child. From then on I knew there was no use in being in prison so we moved back home, purchased our own house."
Popata and his partner Rangimarie own a lifestyle block where they are building papakāinga housing and marae, their own kura kaupapa Māori and further developing their business, Kina Digital.
Their three young children speak only Māori.
"They have no understanding of English. My partner and I believe that if there is strength in their foundation of Māoritanga, meaning te reo and their tikanga, then they will become the perfect product," Popata said.
"True activism is what myself and my partner are doing at home, putting our money where our mouth is and teaching our kids proper te reo, tikanga, how to live, self-sustain ourselves, think entrepreneurial.
"Activism isn't just about getting up on the Harbour Bridge, protesting oil drilling; it's about developing your whānau and your hapū."
As an entrepreneurial couple, they have developed iMāori, an app that teaches te reo and tikanga. It cost them about $50,000 before they received any funding but it now has around 10,000 users with plans to develop it further.
Popata said he was asked by Māori Crown Relations Minister Kelvin Davis to become part of the advisory group after attending a hui in Kaitaia.
"I was the only one throughout of all of hui throughout Aotearoa who stood up and said 'actually, I don't really want a partnership with the Crown. Just give us the resources we need to develop and create our own economy'."
He doesn't advocate separatism, but self-determination or tino rangatiratanga.
"It's what the Māori people really want to strive for but the generation above us have been in that position all their lives, to work in with Government."
They've always depended on the Government. I'm about the real, true self-determination.
"We as Māori have got to remember that this Crown, they were once the enemy."
Even so, last year Popata, along with veteran activist Titewhai Harawira and other members of the Government's Crown Māori relations advisory panel sat alongside Prime Minister Jacinda Ardern and senior ministers in the Cabinet room.
"I think my journey in life was meant to happen," Popata said.
"I was meant to experience going through all that rubbish, hanging out with the wrong people … all the mistakes I've made. I think I was meant to do that because now I'm looking to be a teacher at our kura, and I can give those messages over to our kids."
"I can lead them in the right direction."
"Everyone makes mistakes, that's what I was taught by my father. It's okay to make a mistake but don't make that same mistake again."
