Continuity — The obvious inference here, although the Kzinti apparently are not intelligent enough to see it, is that the race did travel in time to escape being enslaved. "The Warriors" was one of the earliest-written Known Space stories, published well before the author decided to merge various stories into one future history. We suggest it's best to ignore the implication of time travel, which appears nowhere else in the Known Space stories.
Fanfix: We suggest perhaps the species escaped by faster than light travel, which the Kzinti had not encountered at the time. Or perhaps they were just very, very good at hiding; could the species have the psionic power of Plateau eyes? ↵