When you search something in Ubuntu from Unity Dash, you will always get online content search results next to local search results. You will get results from productsearch.ubuntu.com and other third parties like Facebook or Amazon,
If you do not want to see online results in your Unity Dash, you can pretty easy disable this feature. Here is how to do it:
Open “System Settings” from Unity bar, or by searching it in Unity Dash. Then from “System Settings” find and open “Security & Privacy”.
In the “Security & Privacy” screen, click the “Search” tab.
Then on the right side of the “Search” tab, click the “ON/OFF” slider to toggle the option to OFF.
Now close the “System Settings” window.
For the change to take effect you must log out and log in again, or restart the system. Once you will login back any search in Unity Dash will be performed without online results.