Yeah, that is confusing. The 'namespace' term is a bit overloaded in Xperience.
In Xperience there is a difference between the Page Type namespace in the database and the Page Type C# class namespace in your custom code.
The database namespace is whatever you type into the "Namespace" field when creating a new Page Type.
The code that the CMS auto generates for you in the "Code" tab of the Page Type includes the C# namespace
CMS.DocumentEngine.Types as a prefix to every auto generated class, with your Page Type namespace following that prefix.
If you look for your Page Type definition in the
CMS_Class database table, you can see what Xperience considers to be the 'full name' (namespace + class name) in the
Everything before the
. is the 'namespace' and everything after is the Page Type name.