External attendees are displayed as email addresses for the Cockpit email feeds on the Timeline page when the user enters the email instead of the person's name.

From Cockpit We can send emails from CTA to any email address by typing manually even though the email address is not part of person or user object. For such records, we may not be able to resolve to a person or user even if the Email address is present in company person or relationship person object.

In other context, there will be 2 fields that gets resolved when we select person/user from drop down – Email and name.
 

​@ChiragJ