Many internet users suspected the footage was faked using AI or other means when it first emerged, but people close to Macron told AFP it was genuine.
"The president took a moment with his wife (Brigitte Macron) after his speech (on Monday evening). They encountered a group of young people who were singing... so he joined them in a song from the Pyrenees which he knows and loves," they said.
In the night-time video, Macron can be seen reading from his phone the words of "Le Refuge", a song about a lodge in the mountain range on France's southwestern border with Spain, surrounded by men in their 20s and 30s singing vigorously.
The incident might at first have seemed a welcome show of connection with voters for the president, whose reforms including an increase to the pension age have earned him widespread animosity in recent weeks.
But the video was first published on the Facebook page of an organisation called "Projet Canto".
While the group describes itself as preserving traditional songs in digital form, left-wing newspaper Liberation reported last year that it was founded and run by far-right activists and offered recordings of songs with ties to Nazi Germany in its app.
Macron "could not have known in the moment the backgrounds of every person he was speaking to," the person in his entourage said.
The group told Liberation last year that "political songs are part of the history of song, that's why we've stored them," saying it also had "far-left" songs in its catalogue.
Macron previously sang "Le Refuge" during a trip to the Upper Pyrenees in 2022.
