The "single piece" method he is talking about is that the individual _rings_ will be made of a single piece with a single weld, and the rings are then stacked. You can see it already in the Starship under construction in Florida. (Look at the unstacked rings.)

https://twitter.com/FarryFaz/status/1170535411678101504/phot...

https://pbs.twimg.com/media/ED6Tva7XYAESQJJ?format=jpg&name=...