Here is an example of using straw bales to form a concrete house. They stack the bales where the interior will be and then cover them with concrete. Defiantly an alternative form of building but I'm unsure about how permie it is because of the use of concrete.
This isn't so different from the way a lot of old root cellars used to be constructed in this part of the world.
a hole was dug which had a lump in the middle, the desired shape of the cellar to be. Concrete was formed around it and after drying, the dirt was dug out of the middle, leaving the cavity which became the cellar.
I don't know the answers to those questions. I would assume they made the structure safe with re-bar or fiberglass reinforcements although I am not an engineer and can't confirm any of that.
But looking at it again, this structure is probably meant for day use only and not as a permanent residence. There is no kitchen or bathroom.