Not sure who was to blame, Google or SmartThings… but a recent update forced all of your SmartThings device to be linked to Google Home. This was a big problem for me because some of my devices were security related. Namely, unlocking doors, opening my garage doors, and disarming my security system. I had explicitly excluded those functions from Google Home after I discovered I could activate them by yelling at my window which my Google Home was next too. So anyone who knew the trick, could access my home.
Well I just discovered on Reddit this functionality is back, albeit somewhat hidden. To activate certain devices, you have to make sure you are linked to SmartThings in the Google Home app. Then in the SmartThings app, go to Automations -> SmartApps. You will see the Google App there. Selecting the Google App turn off "Allow google Assistat to access all devices and Routines and you will then be able to select which devices Google Home has access too.