Having waited an agonizingly long time to finally post his 200th international sevens try, the winger was relieved to touch down at the London finale of the 2014-15 World Series. He took a pen out of his sock and scrawled his signature on the camera.
"What I had planned to do, originally I had worn an inner vest -- a white vest that was written 'First in Africa' -- but then played the first three games on day one without scoring," Injera tells CNN's World Rugby show.
"I remember the boys mocking me in the changing room, so I took it off, and going into the second day of the tournament I decided I'd sign the ball that I scored the try with.
"So when I scored the try, I signed the ball. Then when I looked up I saw the camera was in front of me, with a lens there -- I went for it."
What Injera didn't realize was that, unlike the TV cameras often signed by tennis stars after a match, these ones didn't have a protective lens.
Still, the ensuing headlines boosted both his profile and that of the shortened rugby format ahead of its Olympic debut at Rio 2016 in August.
After adding two more scores to his tally at last weekend's Hong Kong Sevens, the 29-year-old is now just seven short of the record 230 set by former Argentina star Santiago Gomez Cora.
"It is my dream. When I started playing this game, I remember telling one of the reporters that I want to be the top try-scorer in the world, and they said it's a huge task," Injera says.
"Now that I'm nearly able to realize the dream, it's a huge thing for me and it just shows how far I've come as a player and how far we've come as a team.
"I'll focus on the team, the goals that we want to achieve this season, and hopefully the tries will keep coming."
Kenya qualified for the Olympics at the African regional event last November, despite a late error by Injera that almost gifted Zimbabwe victory in the final.
He has scored 20 tries in 33 matches of the 2015-16 Sevens World Series, in which Kenya is eighth overall with three rounds to play, having blooded several young players ahead of Rio.
"Our goal has always been to medal in the Olympics and I think we are heading in the right direction -- still baby steps," says Injera, whose older brother Humphrey Kayange -- Kenya's former captain
-- is also one of the veterans in the squad.
"We have very many new guys in the team, so one of the main goals was try to get them into the series and have everyone bond and gel.
"The Olympics is the epitome of all sports ... just imagining I'll be there in the village with all these other professional athletes, the likes of Usain Bolt who has always been my role model, it's just great. I'm just happy to achieve."
As well as slick handling skills, rugby sevens requires athletes with the pace of a 100-meter runner like Bolt -- and the strength of wrestlers.
Injera shared some of his exercise tips with CNN: (see video here
The jump squat
"It helps you with explosiveness, and for a player like me who likes running a lot, it helps me to be quicker off the mark," Injera says.
"You have to balance the weight on your shoulders, and you just go down and jump up, then you reset so you won't be able to re-take the pressure on the knees, then you reset again.
"If it's preseason, definitely it's heavier and it's quite a lot of reps, but right now, it's just getting the body ready for the weekend, because your body needs to feel lighter."
The rhythm lunge
"It helps with the directional aspect of the game, because in rugby you don't just run linear, you've got to change direction at high speed," Injera says.
"This one helps stabilize the muscles in your body."
To do a shoulder rotation, push the weight out at arm's length, pull it back into your chest, lift it above one side of your head and around to the other, then repeat the cycle.
"This helps with the shoulders and the chest. The game is not only about running, sometimes you have to go into contact," Injera says.
"This kind of exercise actually helps in fighting through the contact. So I'll be in my athletic position like that and then I'll rotate it and press it out."