The Welsh Highland Railway line was extended to the area from Rhyd Ddu with a grand opening last week.
 
Farmer Philip Hughes said he had been "knocked back" by the incident although he was able to save all his stock.
 
North Wales Fire and Rescue service said it was not treating the fire as suspicious.
 
It said it believed the gorse blaze was caused by a spark which either came from the train or from a discarded cigarette.
 
The Welsh Highland Railway added Police have been consulted and the incident is not being treated as suspicious.
 
"The locomotive has been subjected to detailed examination and the results of this and procedures related to the operation of trains in extreme weather conditions, will be reviewed by Her Majesty's Railway Inspectorate within the next few days," it said in a statement.
 
"Ffestiniog Railway Company steam locomotives are fitted with comprehensive modern spark arrestor systems based on the principle outlined by the Master Mechanics Association of North America.
 
"The railway company has received requests from neighbouring landowners for discussion about the incident and will be contacting them in the next few days."
 
Mr. Hughes said he had lost a "very considerable amount of land" in the fire.
 
"It happened at around 11 in the morning just as an RSPB man had finished surveying a piece of land with Site of Special Scientific Interest (SSSI) status," he said from his home at Rhyd Ddu, near Beddgelert.
 
"He was leaving and I noticed that the train had stopped, it (the fire) took the whole of the SSSI, although the fire service managed to stop it getting into the forest."
 
There has been some local opposition to the railway line but Mr. Hughes said that he was not against the train.
 
"I'm basically for the train, I like these things passing through, but this has knocked me back as you don't expect your land to go up in flames," he added.
 
Safety
 
Mr. Hughes said he managed to get his sheep to safety and the main damage was loss of pasture and fencing.
 
He added he had not decided on his next move, but would wait to see what the train company would do.
 
Welsh Highland Railway general manager Paul Lewin said the company was still investigating the incident.
 
"Our train stopped because they saw a fire and tried to put it out," he said.
 
"When they failed they carried on to Beddgelert because the priority was the safety of passengers."
 
Mr. Lewin said there were around 60 people on the train, and buses were arranged to take them back to Caernarfon, as the train was cancelled for the rest of the day.
 
"The question is whether the fire was started by the train or something else," he said.
 
"I can't comment at the moment, but equipment is being checked, and I will be interviewing staff. We are also talking to the police about a number of things," he added.
 
Mike Owen, the North Wales Fire and Rescue Service county operations Manager for south Gwynedd said he had been in consultation with regards to the potential of fire along the train track.
 
"Due to the nature of train mechanics, and the current dry weather, there is always potential of a fire being caused," he said.
 
"I will be meeting with representatives from the Welsh Highland Railway in the near future to discuss the incident in Beddgelert, and to formulate a collaborative approach to reduce these risks further," he added.
 
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