Take a Paws, page-35201

He use to make the casing's?

Yeh, yeh thats what he did....

Casing's are either "Natural" ....meaning intestines of sheep or pigs, sheep are the thin sausage skins and pigs are the thick sausage skins.
These are becoming less used due to price and consumption of time during the sausage making process but some good butchers still use them, some only use them for their thick sausages as natural thick skins pricing isn't too bad, natural thin skins are a ridiculous price these days.

or

Factory made from mainly collagen which comes from the third layer of the hide from memory. A lot of these are made in Japan.

Supermarkets use the factory made ones mainly but some might not be like some of the thick specialty ones you find in supermarkets.

No Butcher make their own casings to my knowledge unless they grow their own lambs and pigs i suppose.