Contrib statistics: Reported installs and downloads
This is simply due to a bug with the statistics module - see Project Download count Decreased - that has affected Drupal.org infrastructure since the middle of April 2015.

Prior to that bug surfacing, I did not observe a single project where the number of downloads were less than the number of installs.

Just now CKeditor Link is reported to have 487 downloads.  That is 171 less than the 658 reported by the OP in the question (asked two days ago).

Until this bug is fixed, the download statistics should just be regarded as a random number.

As reported by Pierre.Vriens, another bug sometimes affect the installed statistic on the Drupal.org.  This affected many projects a couple of days ago, but seems to have been fixed for most of them today.