The 'Display name' which you may have used for contacts in your Address Book is a personalised option for incoming/outgoing mail which you choose to use and it overrides the actual data in the 'From'. Quick Filter bar search on 'Sender' filter is accessing actual email content and looking for the sender aka 'From' data which matches your search criteria. So if sender did not use a display name which contains the search text or email address does not contain the search text then it cannot locate something that does not exist.