What I find amazing is that we know the position of the star and the orbit of MU69 so well that the occultation was predicted far in advance.
Many stars positions are well mapped. They are guideposts, or reference marks, that essentially define celestial coordinates.
You can find the orbital elements and covariance for 486958 (2014 MU69) here.
It appears that the uncertainty in the size of the orbit is over 2.3876 AU, about 220 million miles! The orbital period is given as 296.44 years +/- 23.88 years. The orbit is based on a series of measurement taken in 2014, over 118 days. I suspect that the nature of the covariance is such that short term uncertainties in angular position cancel. We do not know a lot about the orbit, but we know were it is now, and pretty much how quickly it appears to moving across the sky. IOW it might be on bigger, faster orbit, or smaller slower orbit, the uncertainties are due to the relatively short time we have observed it, but we have enough observations to accurately predict its angular motion accurately for the next few years.