This smells like shared organization being enabled for the organization in question.
Because: If I understood correctly, the CEO of the company was not in CC and thus has nothing to two with the second created ticket, but is member of the same organization.
Please note that shared organization have a great potential for data security issues (and are set to “yes” by default upon creation).
https://admin-docs.zammad.org/en/latest/manage-organizations.html
Our docs need some tidying here, the information can be found underneath the third screenshot and might need further addition to make it even clearer.