Time Machine performing a mobile Backup to a location I can't find anywhere
The folder you're seeing has nothing to do with the network volume you created; it just happens to have the same name. This is a new feature in Lion which keeps track of file changes on laptops when you're away from home so that you still get the benefit of file versioning that Time Machine provides even when your external backup drive is not connected.

You can find more information about this feature in John Siracusa's Lion review at Ars: http://arstechnica.com/apple/2011/07/mac-os-x-10-7/18/