[wahern]

I've wondered the same thing. Also consider that

  [t]he energy released by a cosmic collision increases as the 
  square of the incoming object's speed, so a comet could pack
  nine times more destructive power than an asteroid of the
  same mass. (https://www.space.com/26264-asteroids-comets-earth-impact-risks.html)

ʻOumuamua reached a barycentric speed of 87.71 km/s. The tables on Wikipedia's Impact event article (https://en.wikipedia.org/wiki/Impact_event) assume a speed of 17 km/s relative to Earth. The energy of objects local to our solar system is limited in a way that interstellar objects are not.

With a single observation we can't deduce much of anything concrete except to floor the incidence of these interstellar objects at greater than 0. I'm no astronomer, but I assume models of interstellar objects as they reflect actual risk to Earth wouldn't be very useful without more observations. Whatever the average density in galactic space, I'm betting they're not uniformly distributed. Our solar system is speeding through space that could be littered with clouds of objects.[1] Are we entering a cloud? Leaving a cloud? We can't know without more observations.

[1] There are theories that posit that the ~30- and ~225-million year cycles we see in extinction events are a function of our solar system's orbit in the galaxy, which takes about 200-250 million years. Shorter cycles could relate to the inclination of our orbit (and other stars' orbits) relative to the galactic plane.

[ChuckMcM]

One of the interesting things about the galactic orbit is that our system is not exactly in the galactic plane, so as it orbits it passes through the plane to the other side and then back again.

The kinetic energy of objects is proportional to the square of the velocity (Ke = (mv^2)/2), so an object going 4 times faster than a solar system object has 16 times the energy for the same mass. This makes it possible to have extinction level events from rocks that are 1/4 the size of planet killing asteroids.