Hi pwcutajar,
I'm a bit of a newbie, so I too was having problems. The below could be utter rubbish, but its the way I'm going ( all part of the fun)
I had a quick look in the GitHub repo cloned/listed in the article and found the requirements.txt.
One of the listed requirements is RPi.GPIO & google-oauthlib-tool which is what I think is needed, amongst other things, by the Pi in order to run step 11 (make authenticate). These requirements are installed by install.sh script (Make Install) in Step 1 of 'Setting Up The Assistant ' after they are needed, meaning the Pi doesn't know what to do and you get the error you pasted.
I'm currently setting this up but I'll be going through the requirements and installing them one by one prior to doing anything.
The author probably has this pre installed so had no problems
Hope this helps, more than happy to answer any questions