I predicted something like this happening 3 years ago...
https://www.linkedin.com/pulse/salesforcecom-outage-beginning-end-manuel-breschi/
"... The next level of data disruption I expect to happen some day - at this point probably sooner than later - is when a sales rep will start her working day by handling service requests, orders and any kind of activity and will just realize by the end of the day that those leads were not actually her company's ones, but those of another enterprise, because the same database instance lost the information about the tenant and data would be visible to every customer sharing the same space. Ooppss!"