The capacity to do this has always existed and the circumstances are incredibly trivial.
We used to trust that when reddit said a user wrote X, they actually did write X (excluding hacking). This was a violation of that trust.
Because of the actions of their CEO, reddit was falsely telling everyone who viewed the relevant comments:
> Fluid_Mechanics [score hidden] some time ago
> Fuck /u/spez
While knowing that Fluid_Mechanics had not written that.
(Names have been changed to illustrate the point.)
Lying, and a violation of trust, seem like appropriate terms.