Gareth Huntley, 34, of Leeds, went missing in May 2014 after he set off from Tioman island.
His body was found close to the Juara Turtle project, where he had been living and working as a volunteer.
Janet Southwell, of Bradford, said outside an inquest in Malaysia his death was "definitely suspicious".
"Where he was found it was so close to the turtle project, to the kayak stall and probably 15 seconds walk from the slope where he was found you were in the clearing and you could see a building," she told the BBC.
"So I don't believe he got lost. I don't. I can't. I think it's suspicious."
Inside the courtroom she described her son as outgoing, "incredibly fit" and "healthy".
Rescue team member Lance Corporal Nazrul Izzat Mohd Zaki told the inquest Mr Huntley's body was found in an area they had previously passed by but not searched.
Mr Huntley - who most recently lived in Cricklewood, north London - had been volunteering at the turtle project before starting a new job in Singapore.
Following his disappearance on 27 May a search operation involving up to 100 people began. His body was found in a pond within 300ft (91m) of where he had been working.
He was identified after Mrs Southwell flew to Malaysia to provide a DNA sample.
The inquest, which is being held at Kuantan's coroner's court in Malaysia's eastern Pahang state, has been adjourned and will resume in September.
The mother of a backpacker who was found dead eight days after leaving for a jungle trek in Malaysia has said she considers his death to be "suspicious".