He now has his sights set on upsetting the odds again in Paris.
Should he top the podium, Rousseau will match the Olympic feat of his grandfather Michel who won a sprint cycling gold medal for France in 1956.
That Olympics was in Melbourne, with Rosseau looking to flip the script from a Frenchman winning in Australia to an Australian doing the same in France.
“That would be insane,” he said. “I just found out actually that he won his first gold medal at a world championships the same age that I did.
“Then I think it was two years after that, that’s when the Olympics came around … and he won the gold medal at the Olympics for France in Australia.”
Rousseau came to diving late after beginning his career in gymnastics and sports acrobatics, like his brothers and sisters.
It was never a path he envisaged growing up, given he does not like heights.
“I kind of have a fear of heights and because I’d see the diving on TV and I’d be like, ‘no, I’m never doing that’,” he said, with his mother to thank for steering him towards the boards.
“My sister was trialling for diving and mum asked me if I wanted to try as well and I said, ‘no, definitely not’.
“So mum just pretty much got me out of bed that morning of my sister trialling and she grabbed me and I was kicking and screaming.
“I was like, ‘no, I don’t want to do that, I don’t want to do it’ but I eventually did.
“And then I jumped off the 1m board, the 3m board and ever since then I’ve just really enjoyed doing it.”
A 10m board is a daunting step up from 3m, and one he admitted did not come easily.
“Looking up to the 10m, you kind of tell yourself, ‘oh, it doesn’t look high at all, that’s easy’,” Rousseau said. “But once you get to 5m and then 7m you’re like, ‘oh God, this is really high’.”
Paris will be his second Olympics after Tokyo in 2021, where he came eighth behind Chinese winner Yuan Cao.
For him, those Games were about having fun and soaking up the Olympic vibe rather than challenging for a medal. But it will be a different approach in France as he targets gold.
“I was pretty new to the sport in my first Olympics … so Tokyo was to me just to actually enjoy and feel the Olympic experience,” he said.
“So coming into Paris I’m more able to aim for a medal, I don’t have to enjoy it, I can just focus on competing. All the razzmatazz of the Olympics, that came to me in Tokyo.”