No it is not a live streaming feature..
Rift Streaming means patches can be streamed to while you are playing the game. This means you will only be required to download the bare essentials of the game or of a new patch before you're able to jump in and starts playing.
This went on the PTS today, and appears to be working smashingly, and is expected to hit the live servers with Patch 1.8, or shortly before 1.8.
This can be incredibly convenient if you have a slow connection or if you are brand new to the game. In theory as a brand new player you'd be able to start playing within a few minutes instead of after downloading 10+ gigabytes of game files.
It can also be very helpful if you forgot to patch and it is 10 minutes before raid starts