The app was updated today with a fix for the issue. Microsoft Word documents and other file types can now be viewed directly in in Apple's Files and iCloud Drive apps on iOS 11 and iOS 10 respectively.
Since a previous update to Google Drive earlier this month, the app became the default opener for many file types due to an open-in-place issue.
When users with the Google Drive app installed attempted to open a DOCX file in Files or iCloud Drive, for example, the Google Drive app would automatically open and prompt the user to save the file in that app.
Google Drive version 4.2017.37510 is available on the App Store [Direct Link].