User account picking up incorrect user name
There are two main causes that I can think of.


The person doing the editing was doing it whilst logged in as the other person. Possible scenarios and suggested 'solutions' are:


shared computers where the other person didn't log out when they had finished and the editor didn't bother to sign in as themselves. Solution: Remind all concerned of the importance of logging out when finished and of using their own log in.
The editor is able to masquerade as the other person and was doing so when making the changes
Solution: Remind editor that they should not make changes whilst masquerading as someone else OR revoke their masquerade priviledges.
The editor knows the password of the other person and deliberately logged in as that user. Solution: Get the other person to change their password and keep it private.

The table that links wordpress user to civicrm contact record has become (or was for a while) corrupted so that the wordpress login for the editor is/was linked to the civicrm record for the other person.  (This could happen for a drupal-based site if the uf_match table was corrupted. I presume there is something similar in wordpress, but I don't really know.)