rsync trying to load rdiff-backup

[AC <debusersQ743@acarver.net>]

Due to some version mismatch issues I'm trying to switch over to rsync 
from rdiff-backup for backing up some files on my systems.

On most of them this has worked with no issue but I have one system that 
appears to be trying to load rdiff-backup whenever I run rsync:

root:~# /usr/bin/rsync testfile user@remote.host:testfile
Traceback (most recent call last):
  File "/usr/bin/rdiff-backup", line 20, in <module>
    import rdiff_backup.Main
ModuleNotFoundError: No module named 'rdiff_backup'
rsync: connection unexpectedly closed (0 bytes received so far) [sender]
rsync error: error in rsync protocol data stream (code 12) at io.c(235) 
[sender=3.1.3]


I don't understand why it's trying to load rdiff-backup, the traceback 
is a giveaway that it's running Python but I explicitly called out the 
path to rsync and I know it's not a python script:

root:~# less /usr/bin/rsync
"/usr/bin/rsync" may be a binary file.  See it anyway?
^?ELF^A^A^A^@^@^

This is all happening on Buster but I have three other Buster systems 
that ran with rdiff-backup and I can run rsync fine on them without 
rdiff-backup running.  What's the deal here?