The 'creation user' column in ca_contact table could be a good reference to use.
If the contact has been created via Web Interface, the 'creation_user' column will have the value of the 'userid' of the user, connected to the Web Interface, who created the contact.
The above is valid when the contact is created via Web Interface using: 'New Contact ...' and 'New Contact from LDAP ...'
The 'creation_user' column contains a NULL value when the contact is created automatically during the installation phase.
If instead the contact has been imported via pdm_ldap_import functionality, the 'creation_user' column has an empty value.
It is always better to verify directly in the environment what is the behavior and what is the value of column 'creation_user' when a new user is imported via pdm_ldap_import.