For security purposes when a staff user changes their email address they must verify both the current and new email. For non-staff users they only need to verify the new email.
If a non-staff user changes their email they see the correct message:
We've sent an email to that address. Please follow the confirmation instructions.
However, if a staff user changes a non-staff user’s email they see the (incorrect) staff message:
We've sent an email to your current address. Please follow the confirmation instructions.
As the email was changed for a non-staff user no current address confirmation is required. Discourse correctly sends an email only to the new address, but this message is confusing to staff (who think the user needs to verify the current address).