One interesting thing I learned from this was how they determined the probable size of this comet probabilistically, rather than using direct observation - basically, based on the observations, it could either be really big (10km) or really small (0.5km), and we can basically rule out really big because we've been looking for comets for years, and during that time, to see one that is that big implies that we _should have seen_ thousands that are quite small over that time period, because the size of space objects follows a power law since they're always whacking into each other and breaking up. Since we've only seen one small interstellar object during that time rather than thousands, a large comet is so impossibly unlikely that we can conclude that it is 0.5km in size. I'm sure at some point this will be confirmed in a more conventional way, as well.
What you’re describing is Bayesian inference in action. Given how rare big interstellar comets should be, and how common small ones should be, the lack of detections makes the big-comet hypothesis incredibly unlikely. So we update our beliefs: it’s probably small. Space statistics at work
