I didn't see this animal, but I have no reason to disbelieve either the owner or my mate to whom it was offered. I assume it was the western form of Murray/Darling.
A local farmer was in his 80's & leaving his farm to move into a small house in town. He had a long-term pet carpet which he had caught on the property in his younger days & needed to give away. Nobody wanted it 'cos it was eleven & a half feet long, so he had to let it go. A mate of mine went out to pick it up, but declined when he saw the length of it. The owner said it was 4 or 5 feet long when he caught it 30 years prior. The owner's wife verified this.
Each autumn he would put it in a wheat bag & tie it off twice with bailing twine & put the bag in a box under the bench in his shed & take it out again in the spring. Don't know what he fed it on, or if it was in an enclosure, but most carpets on properties are kept in the feed shed & left to fend for themselves as far as food goes.
I do know that the ones which were inhabitants of grain sheds on places where I worked as a kid were big enough to scare the ****** out of me. They had no human interference & lived on rats, mice & slow cats.