"Kissing", "contact", and photos of objects like Arrokoth are too misleading.

The Earth/Moon and Pluto/Charon situations started with extremely high speed collisions (plenty of kinetic energy) between separate bodies. Those collisions were spectacular sideswipes (vs. head-on), so there was also a huge amount of rotational inertia. That's another must-have, to end up with two bodies orbiting each other.

It was not well explained in the article, but the simulation timestamps indicate that it would all have happened just over sixty hours or so. So a comparatively short kiss during which a lot of dynamic stuff was still happening.

It would also be interesting to know how the orbits became quite circular afterwards (relative to the common center of mass).

Presumably from tidal forces, from the differential of the gravity field in the presence of nearby massive objects (like the sun, or jupiter).

It could be largely a redistribution of rotational energy in the system. Where they contacted could not particularly stable, heat would be generated, energy dissipated. maybe ice state change helps, with luck a messy rolling contact could become a series of slingshot orbits, but I am just making stuff up here