You see that it is adivsed to create your file with your app-specific mime type. Is it right way? I wonder because google drive somehow associates files with the application that created them for Open with functionality. Can this be exploited for the file picker?
FYI-- You mentioned your project ID being alpine-dogfish-833. If you login to the developer console, then click on your project (which takes you to the project "Overview" page), you will see 2 identifiers at the top: Project ID: alpine-dogfish-833 and Project Number: 1088706429537. "Project Number" == "App ID" == "the numeric prefix on the Client ID"