The mystery object is
both an asteroid and a comet. A comet is an electrically active (discharging) asteroid. An asteroid is a comet without a sufficient charge differential to be electrically active. Otherwise, both are rocky /metallic in various proportions, relatively small bodies in our solar system. Some comets have short periods, some have long periods, and some seem to have no period because their hyperbolic orbits imply that they depart the solar system after rounding the Sun (or disappearing into it).
The elongated elliptical orbit with high eccentricity used to be a calling card of comets, but the presence of comets orbiting "nicely" in the main asteroid belt make the orbital shape no longer such a great distinction, and of course some perfectly normal asteroids have Earth-crossing orbits that definitely puts them out of the more circular main belt orbitals outside Mars. Of more interest might be the question, "why does this or that otherwise "normal" asteroid occasionally light up like a comet when its neighbors apparently do not?" Coma and jets and tails aside, The EU interpretation is that there appears to otherwise be no difference between a cometary body and an asteroid body, short of the electrical condition.
I used to believe that to be a comet, the body had to traverse a great voltage differential in order to "light up" - such as from the theorized Oort Cloud or deep in the Kuiper Belt and in toward the Sun, but seeing reports that main belt orbiting bodies occasionally also light up makes me wonder what the cause is, in those cases.
And collisions? Still exceedingly rare, or so gentle as to avoid observation, in most cases. Popular among astronomers and copy writers, but apart from small bodies (bolides, asteroids, occasional comets, dust grains and the like) impacting MUCH large bodies (planets, larger moons, Stars), collisions in space are really rare. At the smaller scales, things are just large distances apart, and in plasma motion they may be following fairly collimated paths, for the most part. At larger scales, fairly stable orbital conditions generally have been established, and big things do not go bump in the night, as a very general rule. Never say that they can't or won't collide - that's hubris and leads to Black Swan events - but I could list the number of verified stellar and planetary and moon collisions on the back of a napkin without anything to write with. Death spirals of binary neutron stars? >snork>! Colliding galaxies? Look good in simulations. I don't think that verified proof that any two suspected galaxy "collisions" exists simply because our distance estimating procedures are now so suspect that we hardly know where things are
, any more, once they are out of Hipparcos's parallax reach (which is well inside our neighborhood of our galaxy only). Other than educated guesses, I think we do not actually know how far we are from our galaxy's center. Guesses can be dead on, and they can be wildly off, when it comes to galaxies.
So, comets = asteroids + electromagnetic phenomena, and they don't whack together and explode. As a rule.