O365 Deployment - Branch Option Triggers Download from Microsoft Update

I'm testing deployment of Office 365 2016 ProPlus.

During installation, specifying the Branch="xxx" option in the configuration file triggers a large download from Office 365. 

Whereas if I omit the Branch="xxx" option, the install takes place from the cache within the local setup directory (i.e. Office\Data).

Any ideas on whether if this is expected behavior or a bug?

The Reference for Click-to-Run configuration does not indicate that we should expect a download from Office 365 when specifying the Branch option:

https://technet.microsoft.com/en-us/library/jj219426.aspx