This is pretty bad. That pretty much destroys the credibility of Reddit's commenting system in a single act. No one can look at the integrity of the comments written by others the same any more.
We already know that Reddit was originally filled by sockpuppets, so more deceptive behavior from reddit higher-ups today doesn't surprise me too much...although this isn't really deception, this seems more like admin trolling.
Sockpuppet is one thing. Altering a user's comment to frame him/her is another thing. Basically any comment cannot be trusted anymore. It takes years to build trust. It can be destroyed in an instant.