Good point. One thing we learned from exoplanet hunting is that there is a much greater diversity out there than we had originally thought, implying that planet

Good point. One thing we learned from exoplanet hunting is that there is a much greater diversity out there than we had originally thought, implying that planet formation is a lot more of a dynamic process than our previous models indicated. Prior to the discovery of exoplanets our planet forming models were very much "over fit" to the example of our own Solar System, giving the impression that other stellar systems would end up looking similar to our own. The reality is that our Solar System is, as you say, probably unusual. One aspect of this is that it seems like planetary migrations are pretty common (both inward and outward). If that sort of thing happens early during planet formation then it could easily explain an "asteroid" (which we understand is almost certainly a planetessimal fragment, though many asteroids are just that) which has acquired additional material including ices. The obvious followup here is that we need way, way more closeup observations of small bodies in our own Solar System, we probably also need to develop better techniques for observing interstellar interlopers, and we need to improve our studies of extrasolar planetary systems. Fortunately the first part is already covered, between the Hayabusa 2, Osiris-REX, Lucy, Psyche, and New Horizons missions we should collect a lot more information on such bodies. However, it's probably going to be a long time before we have answers even to simple questions like the formation histories of most small bodies in stellar systems and what the "average" stellar system looks like.