There are some checks that happen in the background, which can cause the email to be marked as Opened and/or Clicked, even though the email is undelivered.

For example, if we try to deliver an email and find that the mailbox does not exist, it can cause an NDR (non-delivery response, often referred to as a bounce). This can cause an email to be both marked as clicked or opened and bounced at the same time.

This can also happen if the organization you are sending to uses security or caching services that will look at all incoming emails (even before an attempt to deliver it is made), which would trigger the email to be marked as "Clicked" or "Opened". A company may do this to see if there is anything malicious in the email.

Since the system can't differentiate between a real user and these security systems, we can sometimes see these clicks and opens on an Undelivered email, but the used credits for those prospects will still be returned since the email is marked as Undelivered.