Scott was 22 at the time. A young man, but one with the belief that comes from being places, doing things, and winning medals.
The Rio Olympics three years previously had yielded a couple of relay silvers. World team medals followed the year after. Then he returned from the 2018 Commonwealth Games with sixth different slabs of metal around his neck.
The Covid delay to his second Olympics only deferred more success, with 4x200m freestyle gold accompanied by silver in the 4x100 medley.
Perhaps more pertinently, silver also came in individual events, Scott finishing second in both the 200m freestyle and the 200m individual medley.
He will complete in the same two events again in Paris, as well as in a couple of the relays, but it seems there is something different about this version of Scott.
Look at interviews with him at the time of Tokyo and there's still a shyness. His voice is softer. His answers fleeting. His gaze rarely held for long.
Contrast that to now. Still quiet, but forthright. Confident enough to take on difficult topics, such as gender issues in sport, the importance of learning to swim, and pool closures.
And self-assured, too. Earlier this month, he stopped a BBC interview part way though to check on a disturbance at the other end of the room. It spoke to his professionalism, his attention to detail and his discipline.
Talk to those who train with him at the University of Stirling and those words are among the few they let slip. Under the condition of anonymity, of course.
One describes Scott as "the hardest worker I've ever seen". Another considers him "enigmatic, a great guy but one who changes when he goes into competition mode". A third speaks about how he "demands standards and leads by example".
Fellow Team GB member Katie Shanahan picks up on the latter, explaining there is not a training day that goes by when she doesn't learn something from Scott.
"I’m so grateful I can swim with him every day," she says. "He’s given us so much good advice and I know how much work he puts in."
Yeah, but what is he really like?
"He’s… just Duncan. I don’t know how to describe him," the relentlessly chatty Shanahan says, stuttering. "I’m lucky that I get to see the human side of him, and he’s just a really nice guy. He’s funny, and very down to earth."