Even standard files on iCloud. Who knows how important the average users' cloud files are to them? (I don't use public cloud storage at all anymore because of this exact fear - what if some arbitrary billing/transaction error locks me out of everything without recourse?).
To be fair I've no idea what the person in question got their account locked for and if there was any shadiness involved but I doubt they'd write about it publicly (or get access restored) if there were, which implies that at any time your account and your data can be taken away for something entirely mundane.
It makes me really concerned in fact how Google would handle something similar to this - given that for Chromebook users everything (literally EVERYTHING you would normally do locally on a computer) is in/via your Google account.