Moving Table To New File Group

Hi all

I have a table called ACTIVATION_CONSUMPTION which is in PRIMARY file group, in order to move this table to new file group [FG_ACTV], I have done the following

1. ALTER DATABASE [MYDB] ADD FILEGROUP [FG_ACTV] (i have not attached a file to this file group)

2. IF EXISTS (SELECT * FROM sys.indexes WHERE object_id = OBJECT_ID(N'[dbo].[ACTIVATION_CONSUMPTION]') AND name = N'ACTIVATION_CONSUMPTION_PK')
ALTER TABLE [dbo].[ACTIVATION_CONSUMPTION] DROP CONSTRAINT [ACTIVATION_CONSUMPTION_PK]
GO

3.ALTER TABLE [dbo].[ACTIVATION_CONSUMPTION] ADD CONSTRAINT [ACTIVATION_CONSUMPTION_PK] PRIMARY KEY CLUSTERED
(
[ACTIVATION_CONSUMPTION_ID] ASC
)WITH (PAD_INDEX = OFF, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, ONLINE = OFF) ON [FG_ACTV]

The above command executed successfully and now the table is in new file group [FG_ACTV]

My question is how come the table was moved to new file group though it has no files attached to it?

Thanks in advance.