Contrib statistics: Reported installs and downloads I've noticed that the number of reported installs is usually (not always) somewhat larger than the number of downloads. I figured maybe this is because of multi-site installations in which one download runs on several sites. On the other had, there have to be cases where a module is downloaded and not implemented in production, which perhaps would account for cases where there are more downloads than installs.

But I just noticed that "CKEditor Link" has over 50,000 reported installs and only 658 downloads. That doesn't make any sense. Does anyone know what's going on there?

These statistics are relevant to the decision of which modules and themes to use in a system. (Edit: They are relevant for me because I can't afford to be in a situation where my sites go down because a Drupal revision breaks a module and the module maintainers don't get it fixed pronto. This is much less likely to happen with an installed base of 50,000 than 500.)
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.