I doubt it was snapshotting. It is common to force OS updates. For macOS there are tools where the employee will be prompted to update, and can dismiss for a while, but eventually they will be forced to restart. My guess is that the Facebook employee had ignored update prompts and was then forced to update. Every day does seem odd, I can't think of an update type that would require restarts/logoff every day. At least a couple years ago Facebook and Dropbox were managing their Macs in similar ways, with similar tools, I'd be surprised if they changed to something that required daily restarts.