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It sounds like notes on your devices may have synced when the email account was added, as described here:
iOS: Syncing Notes
Notes are associated with an IMAP email account or iCloud account. To sync Notes, enable Notes for each account in Settings > Mail, Contacts, Calendars or Settings > iCloud.
You can stop syncing notes by tapping Settings > Mail, Contacts, Calendars or Settings > iCloud, tapping the email address that you added, and switching Notes to the off position.
Additionally, if your husband has backed up his iPhone to iTunes or iCloud, the steps in this article can help with recovering the lost notes from his device:
iOS: Back up and restore your iOS device with iCloud or iTunes