That got me interested, too.
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"Based on observations spanning 34 days, ʻOumuamua's orbital eccentricity is 1.20, the highest ever observed. An eccentricity exceeding 1.0 means an object exceeds the Sun's escape velocity, is not bound to the Solar System and may escape to interstellar space.
While an eccentricity slightly above 1.0 can be obtained by encounters with planets, as happened with the previous record holder, C/1980 E1, ʻOumuamua's eccentricity is so high that it could not have been obtained through an encounter with any of the planets in the Solar System. Even undiscovered planets in the Solar System, if any should exist, could not account for ʻOumuamua's trajectory nor boost its speed to the observed value. For these reasons, ʻOumuamua can only be of interstellar origin." Wiki
Average speed of Oumuamua = 5.55 AU/year relative to sun (per wiki)