I feel that's taken a little out of context. There were two trials:
> For No-imagine trials, participants were given one of their cue words, asked to first acknowledge the event in their mind. Then, while continuing to stare directly at the reminder cue, they were asked to stop thinking about the event – they should not try to imagine the event itself or use diversionary thoughts to distract themselves, but rather should try to block any images or thoughts that the reminder might evoke. For this part of the trial, one group of participants was given their negative events to suppress and the other given their neutral ones.
Emphasis added. And the trial you refer to:
> For Imagine trials, participants were given a cue word and asked to imagine the event as vividly as possible, thinking what it would be like and imagining how they would feel at the event. For ethical reasons, no participant was given a negative event to imagine, but only positive or neutral ones.