[rachofsunshine]

Any object that approaches the Solar System from interstellar space is necessarily moving at least (solar) escape velocity. It's "falling down" into the Solar System's gravity by a distance equal to how far it has to "climb up" to get away in a system with little appreciable friction.

The paper assumes 100 km/s, which is more than double the solar escape velocity at Earth's orbit. The mass doesn't make a difference in the absence of friction and assuming it is much less than the primary body; escape velocity depends only on the mass of the primary.

There would be some "friction" (since the hole would be eating up small amounts of mass on its journey and that mass would be moving at less than solar escape velocity), but without doing any calculations I'm almost certain it's nowhere close to enough to slow it down.