My dogs and my cat do NOT peacefully coexist. Never have. The difference though is that Amelie is wary of the dogs and is a timid cat in general, so she just stay away...gets on a high place that they can't reach and watches them disdainfully. There has never been any situation unless SHE has felt cornered, and then it was less about attack and more about stealth and trying to get away.
I think you need to just observe for a while. You don't know what led to the incident, so this could just be a random, atypical situation that won't repeat. No sense focusing on how how to fix it if it's not gonna happen again anyway.