I used the built-in download tool to download Windows10.0-KB3081448-x64.msu 
I selected the folder where the updates (x64) were located, run WinReducer, when it's done I did a test install in VM. When I click on the same update file I copied to a flash drive, it still installs the update.... that means the update wasn't slipstreamed..

WinReducer EX-100 - v0.4.3.0