A local resident told reporters he was "so sharp" but very protective of what was inside the home.
"You only had to get close to the yard and he already sent you away. He kept an eye on everything with binoculars.
Another neighbour said they sensed that something was wrong inside the home surrounded by security cameras and guarded by a large fence, but didn't know what it was.
"Even when he was gone, we heard noises there. From a lawnmower for example. So there must be someone else. But no idea who.
"What was special were all those cameras around the house. And yes, then there is that closed attitude. No one here had contact with him."
A man who lived near the woodworking company where he worked told the newspaper he was "extremely friendly but difficult to reach, with a large bundle of hair and a thick beard.
"I took packages for him, tools and the like, but I found it annoying that I could reach him so badly by telephone," he said.
Local mayor Roger De Groot said it was believed the children's mother had died.
"As far as I know their mother died before they arrived there," he said.
"Police found makeshift living quarters where the family was living in hiding. I've never seen anything like it."
The children are believed to have existed without the knowledge of authorities or neighbours at the remote farm hidden behind trees with an access road crossing a bridge that is hardly visible from the main road.
According to local reports, the family had been surviving on vegetables and animals tended in a secluded garden.
A neighbour confirmed to local media that only one person had been seen at the premises over the years.
He told Dagblad van het Noorden he was "totally surprised" to hear an entire family had inside the home the entire time he lived next door.
"I am shaking on my legs," he told the newspaper.
A local postman said he had never once delivered any mail to the home.
"It's actually pretty strange, now I come to think about it," he told Algemeen Dagblad news website.
The siblings were receiving treatment at an undisclosed location, the mayor said at a press conference on Tuesday.
"I understand there are a lot of questions," de Groot said. "We have many too. The police are investigating all possible scenarios.
"The family is in a safe place. They need rest."
An employee at the pub told RTV Drenthe the young man who escaped the basement looked scruffy and bewildered with long thick hair when he approached him.
He said that before the young man told him the story and asked for help, he ordered and drank five beers.
"He was very confused," Chris Westerbeek told the broadcaster.
"You could see he had no idea where he was or what he was doing. He said he had run away and that he urgently needed help.
"He said he had brothers and sisters who lived at the farm. He said he was the oldest and wanted to end the way they were living."
The 25-year-old told the publican he had never been to school and that he escaped at night because it "was not possible during the day".
When police attended, they arrested the 58-year-old man. Police said he was uncooperative.
"A young man reported to us because he was worried about the living conditions of his family," police said in a statement.
"That is why we went to this address. We found six people in a small room in the house that was closed off.
"It is unclear whether they stayed there voluntarily. These people may have been staying on the site since 2010.
"As it seems, they are not registered in the municipal basic administration. They have indicated that they are of age. This will of course be further investigated.
"They say they are a family, a father with five of his children. They have been examined by a doctor. We naturally have care and attention for the family.
"The arrested man concerns the tenant of the building. We do not yet know what the relationship is with the other people. This is part of our research. He is locked in for interrogation and is still detained."
