Chaostic is simply a sexual/romantic orientation that cannot be pinned down into one specific attraction. Similar terms that could help to describe this orientation would be Abrosexual, Duosexual, Gendercollector, and Pomosexual. Let's say that you have an idea of what your sexuality is, but it always changes/fluctates, so you'd hoard those terms, That's where the relation to duosexuality comes in, You have multiple orientations that you identify with, and you don't stick to one of those orientations.
It is basically sexuality-collecting, and for those who are uncomfortable using one term to describe their sexuality. Some of their attractions may be more common so they'd feel more comfortable with using that term, but they still have a connection to other sexualities.
If you're still confused, let's say someone identifies as uranic, omnisexual, demisexual, androsexual and toric. They use multiple terms because they cannot pin down exactly what their sexuality may be.