Another instructor at CCSF contacted me today, to see something strange on her iPad. Her Google Drive app suddenly showed another employee's drive, someone who had never used her iPad or authorized it to see her files.
I opened that account and saw this, with the filenames and account names redacted. The three accounts in the lower left pane are the correct accounts, and the one at the top ending in "mail.ccsf.edu" is the other person's account.
All this other person's files and folders were shown, like this.
The immediate problem was fixed by taking the iPad to that other person, who removed the account from it, but this leaves unanswered the question of how this happened in the first place.
I didn't find any reports online exactly like this, but this article is somewhat similar:
The day that Google Drive broke my trust
If I learn anything more, I'll add it to this page.