It's a restricted shotgun because it is written so on the registration certificate, relevant or not that's a fact.
And yes the gun is factory made in this configuration.
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It was not reduced to that length by changing anything, it came direct from the factory in this configuration, it never had a stock to begin with, and the barrel was always at that length 10" .
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"Otherwise" is an expansion upon "folding, telescoping" not an all encompassing god term. It's saying "we can't think of any other words to describe a collapsible stock, so basically anything that is similar to these other two is described here".