BC does not magically change product and catalog information. The only way that would have happened is as you point out if that data has been changed. You can view the audit logs to see when they were changed.
If you did an import via CSV and the information is all old data then that will be the method at which this was all changed.
You can view the admin logs and audit logs. If you see lots of products edited at the same time by one of their users, then the client did it.