Google has traditionally embraced an open culture so accessing documents outside the scope of your job has traditionally been totally fine & is the stated reason why every full time employee is considered an insider for trading purposes, with legal restrictions imposed on when you can trade.
'm guessing from memory (& this would be from before my time so ex-Googlers with a better memory please remind me), but the data policy was introduced to deal with SREs looking at customer data they weren't supposed to, not about the work product of coworkers.
In terms of people's calendars I'm totally confused - it's super-easy to change sharing permissions even on a per event level. Sounds like it's a pretext - the reasonable approach would be A) Improve training about the available privacy settings B) Improve Google Calendar to make it easier to manage those privacy settings since I'm sure other workplaces have a similar problem.
So the calendar stalking is the bigger problem I think on the part of the fired employees but the "accessing documents outside the scope of their jobs" is total BS. The leaking "sensitive business or customer information" seems like pure FUD - seems like a lawyer-approved way to slander about what happened.
I'm really curious whose calendars were accessed "inappropriately" and who reported feeling threatened. Moreover just accessing a calendar is not something you're notified about so that would indicate this is either BS on Google's part or these people were doing a bit of active stalking on the side. Could come out that everyone is the asshole in this story but given how bad management/labor relations have gone under Sundar, I'd wager that Google is definitely engaging in really shady shit on their own here.