"I'm just buzzing."
He was attending a Warriors training at Mt Smart Stadium, and had no idea what was going to happen.
Kehu was handed his Red Bull branded cap by expedition kayak athlete Ben Brown, and his Red Bull surfboard by Johnson.
His father, Khan, said Red Bull scouts had had their eyes on his son since he was 13 or 14.
Claiming both the U16 and U18 national titles last year and his success in pro junior competitions, "it kind of sealed the deal", he said.
"They've done so much for me already, they've got my back for sure," Kehu said.
Red Bull would help with Kehu's travel costs to competitions, as well as a supply of surfboards.
Kehu now joins a team that also features top international surfing professionals such as former world champion Mick Fanning, Jordy Smith and Jamie O'Brien.
Red Bull sports marketing manager Brendan Thomas said they had been keeping an eye on Kehu since early 2012.
"For us, we don't jump into a partnership without really knowing the potential and personality of the athlete.
"And with Kehu we have seen the potential," Mr Thomas said.
After receiving "expert opinion", they decided it was time for Kehu to join the Red Bull team.
Mr Thomas said Kehu was now sitting among some of the world's best surfers, with only "very small athlete pool selected to wear Red Bull".
"Now Kehu is right up there.
"It'll open a lot of doors and opportunities for him," Mr Thomas said.
Kehu's father said his son's selection was "pretty exciting".
"We are all really stoked, the whole family are," Mr Butler said.
"Red Bull means a foot in the door, he's been on the radar for a while."
Red Bull sponsored surfers:
Mick Fanning: Professional Australian surfer Mick Fanning won the 2007, 2009 and 2013 ASP World Tour, and last year made headlines around the world after surviving an encounter with a great white shark.
Jordy Smith: South African professional surfer, Jordy Smith competed in the World Championship Tour, and won the 2007 World Qualifying Series.
Jamie O'Brien: Hawaiian freesurfer Jamie O'Brien gained wildcard entry into the Pipeline Masters and won at age 21, and now spends time filming surfing in amazing locations.
Kehu Butler: Tauranga surfer who claimed both the New Zealand U16 and U18 national titles last year.