10777 - Dimension table indexes

Hi experts,

i am reading about
Dimension table indexes:
Create a nonclustered primary key index
Create a clustered business key index

but i do not understand
Create a nonclustered primary key index
why nonclustered?

this is the script
CREATE TABLE DimProduct
(ProductKey int identity NOT NULL PRIMARY KEY NONCLUSTERED,
 ProductAltKey nvarchar(10) NOT NULL,
 ProductName nvarchar(50) NULL,
 ProductDescription nvarchar(100) NULL,
 ProductCategoryName nvarchar(50))
GO

 CREATE TABLE DimGeography
 (GeographyKey int identity NOT NULL PRIMARY KEY NONCLUSTERED,
  PostalCode nvarchar(15) NULL,
  City nvarchar(50) NULL,
  Region nvarchar(50) NULL,
  Country nvarchar(50) NULL)
GO

 CREATE TABLE DimCustomer
(CustomerKey int identity NOT NULL PRIMARY KEY NONCLUSTERED,
 CustomerAltKey nvarchar(10) NOT NULL,
 CustomerName nvarchar(50) NULL,
 CustomerEmail nvarchar(50) NULL,
 CustomerGeographyKey int NULL REFERENCES DimGeography(GeographyKey))
GO


 CREATE TABLE DimSalesperson
(SalespersonKey int identity NOT NULL PRIMARY KEY NONCLUSTERED,
 SalesPersonAltKey nvarchar(10) NOT NULL,
 SalespersonName nvarchar(50) NULL,
 StoreName nvarchar(50) NULL,
 StoreGeographyKey int NULL REFERENCES DimGeography(GeographyKey))

 CREATE TABLE DimDate
 (DateKey int NOT NULL PRIMARY KEY NONCLUSTERED,
  DateAltKey datetime NOT NULL,
  CalendarYear int NOT NULL,
  CalendarQuarter int NOT NULL,
  MonthOfYear int NOT NULL,
  [MonthName] nvarchar(15) NOT NULL,
  [DayOfMonth] int NOT NULL,
  [DayOfWeek] int NOT NULL,
  [DayName] nvarchar(15) NOT NULL,
  FiscalYear int NOT NULL,
  FiscalQuarter int NOT NULL)
GO
  -- CREATE A FACT TABLE
  CREATE TABLE FactSalesOrders
  (ProductKey int NOT NULL REFERENCES DimProduct(ProductKey),
   CustomerKey int NOT NULL REFERENCES DimCustomer(CustomerKey),
   SalespersonKey int NOT NULL REFERENCES DimSalesperson(SalespersonKey),
   OrderDateKey int NOT NULL REFERENCES DimDate(DateKey),
   OrderNo int NOT NULL,
   ItemNo int NOT NULL,
   Quantity int NOT NULL,
   SalesAmount money NOT NULL,
   Cost money NOT NULL
    CONSTRAINT [PK_ FactSalesOrder] PRIMARY KEY NONCLUSTERED
 (
      [ProductKey],[CustomerKey],[SalesPersonKey],[OrderDateKey],[OrderNo],[ItemNo]
 )
 )
GO