A 33-year-old Frenchman, who has not been named, was taken into custody following the shooting on Wednesday afternoon. He now faces manslaughter charges.
Mr Keane is believed to have been looking after his younger brother in their home after their father died earlier this year following their mother’s death.
The ex-pat community in nearby Cajarc were organising an anti-hunting protest march on Friday.
Family friend Rose Dodd said: “Yesterday afternoon my son's best friend Morgan Keane aged 25 was shot and killed by hunters while gathering firewood near his house.
“We are holding a march in his memory against these senseless killings."
Lilliane, who asked to be identified by only her first name, told local media that Mr Keane "had been very close to his parents".
She added: “He cared for his mother, and stayed at his father's bedside and watched over him until the end.”
Gavin, her husband, said: “Morgan was always helpful. When I asked for help on a job site, restoring a building, he was always there.”
In a tribute on Facebook, she wrote: "Michael's best friend and our surrogate boy was accidentally killed by a hunter last evening.
"He leaves a brother of 21. His dad died this year and his mum a couple of years ago.
“This is the saddest thing that has ever happened to me.”
Watch: Thousands Protest in French Cities Over Proposed Security Law
Didier Burg, the Mayor of La Garrigue, said Mr Keane “lived with his brother, and was a quiet and very nice youngster.”
“They are friendly, nice boys," said a near neighbour. "Everybody is in a state of shock – this is a terrible tragedy..”
A spokesman for the Cahors Public Prosecutor's Office confirmed that it has since “launched an inquiry for manslaughter.”
"The gunman thought he had identified a wild boar.
“But his shot caused the death of this young man who was not taking part in the hunt,” Frédéric Almendros, public prosecutor in Cahors, told French media.
An investigating source said of the incident: “It happened while a boar hunt was passing by the edge of the village just before 5pm on Wednesday.
“The victim was chopping wood outside his home when a stray bullet hit him.
“The emergency services arrived soon afterwards, but they found that the young man had died on the spot.”
He added the hunter had a licence, was sober and was “mortified” by the killing.
The death came the day after a hunter was sentenced for shooting Welsh mountain biker Marc Sutton, 34, dead in the French Alps in 2018.
He was cycling in thick woodland on a "well used" path when he was hit by a stray bullet fired by then 22-year-old hunter Lucas Clerc.
Clerc was sentenced on Tuesday after he admitted firing the fatal shot, which he said was intended for a wild boar.
He was sentenced to a total of four years, three of them suspended, banned from owning a gun for five years, and banned from hunting for ten.
Mr Sutton had lived with partner Jo Watts in the Haute-Savoie region of France for four years before he was killed on October 13, 2018. The couple were well-known locally as the owners of two restaurants, one of them vegetarian.
An investigation found that Mr Sutton had been wearing high-visibility clothing and that visibility was good at the time he was shot.
Two other hunters were charged with concealing evidence when it was revealed they put up safety signs after the fatal shot was fired.
For the 2019-2020 hunting season, there were 141 accidents in France of which 11 were fatal, protesters said.
Watch: France mourns ex-president Giscard as reformer, European