Again:
the simple act of refusing to leave IS belligerent.
When your kid lays on the floor refusing to move is that belligerent? Of course it is. When college students stage a sit in are they being belligerent? Again, of course. It is quarrelsome, antagonistic, and contentious, behavior. Period. You don’t have to be making noise or being physical, the direct act of refusing to comply IS belligerent.
Again, Oscar Munoz would not have gone on the public record saying Dao was totally innocent of wrongdoing if Dao had been belligerent. Munoz specifically noted that Dao was seated in his assigned place, and had every right to be there.