Taken to the opposite extreme, I think it's in some sense obvious that some degree of suppression is actually good for you, precisely because ruminating for long periods of time is clearly bad for you.
From a neurological point of view, why should we see reiterating negative thoughts as any different from reinforcement learning? If we revisit these negative topics, are we not strengthening their presence in our minds?
That said this study does not sound like it proves that suppressing negative thoughts works over a long period of time. The original theory posits that these suppressed thoughts might cause problems even years later when the latest this was followed up was a period of three months. So grains of salt etc.