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       use chroot
              If  “use  chroot”  is  true, the rsync daemon will chroot to the
              “path” before starting the file transfer with the client.   This
              has the advantage of extra protection against possible implemen‐
              tation security holes, but it has the disadvantages of requiring
              super-user  privileges,  of  not  being  able to follow symbolic
              links that are either absolute or outside of the new root  path,

and later:

              hierarchy.   The  default  for  “use chroot” is true, and is the
              safer choice (especially if the module is not read-only).

This feature is activated if you run rsync in daemon mode, which seems
to agree with your results.