Victorian teen survived against the odds

Carly Waters, Christine McGinn

William Callaghan may have survived his ordeal so well partly because he did not realise he was in so much strife.

While the noise of the helicopters and motorbikes looking for him were probably overwhelming, experts also note the teenager was used to bushwalking and was well clothed.

William, who is non-verbal with autism, provided what might be the good news story of the year when he was found on Wednesday in harsh Victorian bushland.

He went missing on Monday at Mt Disappointment, after becoming separated from family members, and spent two freezing nights in the bush with no food or water.

Mansfield Autism Statewide Services director Simone Reeves has worked with William and his family for several years.

Ms Reeves said when children first came to the facility they were often highly anxious, which would affect their learning, so exercise such as bushwalking was often used as a way to mitigate any stress.

Ms Reeves said William would not have known he was missing.

"(He) wouldn't have known that his parents didn't know where he was, so he wouldn't have been particularly worried," Ms Reeves told AAP.

"He thinks what's in his mind is in their mind as well."

William would have faced the same challenges as anyone to the harsh weather conditions, but the sound from the search and the crowd looking for him may have overwhelmed him.

"Noises for him are very difficult, so when the motorbikes and helicopters were going it could have been very scary for him," Ms Reeves said.

Bob Cooper is a survival instructor who has more than 40 years experience, and says the Victorian bushland can be extremely dense and render people completely camouflage.

The survival expert said the most worrying thing when William went missing was him catching hypothermia given the below zero temperatures.

"It was lucky William was dressed reasonably well in those cold conditions," Mr Cooper told AAP.

Mr Cooper said children did not carry the same fears adults did, especially in settings like the bush where everything can be seen as an adventure.

Ms Reeves said children with autism process traumatic events differently, but she is optimistic William will recover from his two-day endeavour.

"He didn't understand that other people were so worried about him, so we're quite optimistic that he will move forward and will not be affected emotionally by this," she said.

"But he will obviously need to be monitored and he has a very supportive family."