I think I found a errata on chapter 1, page 38, section “Importing Packages” it says:
As you did before, to keep things tidy, single click the newly generated Materials folder (in the Models folder) and rename it to Models. Drag this new folder into the parent-level Materials folder.
Do you mean, move the contents of Materials folder (in the Models folder) to the parent-level Materials folder and delete Materials folder (in the Models folder)?