Long story short, if you can collapse, or shorten a firearm from greater than 660 mm to less than 660mm it is a restricted firearm.
If it starts off shorter than 660 mm and can't become shorter it is non-restricted as long as it doesn't meet any of the prohibited criteria or the other restricted criteria (semi-auto centerfire barrel length, or handgun)
That is a fixed stock firearm that can't be folded or telescoped to less than 660, that is not a prohibited firearm, not a handgun, can't discharge centerfire ammunition in a semi-automatic matter with a 470mm less barrel length. It's non-restricted
The short hand of the law for simplification is 660mm OAL is the minimum, but really it's really can't make it shorter than 660 mm, via folding telescoping or otherwise.