His argument regarding the trajectory into our Solar System is pretty flaky. It completely disregards Hopkin's computation of a "steep entry angle" and supposition that it comes from the "thick disk", instead assuming the incoming trajectories of interstellar objects are uniformly distributed across the celestial sphere.

Mass distribution in our galaxy is decidedly anisotropic - most mass lies in the galatic plane.

Loeb's estimate of the comet size is strange, when two observatories concur that the maximum size is around 10km.

Look at https://news.ycombinator.com/item?id=44713579 for links to real science.