No, why would you think that? One can model in UML anything between a bunch of classes, to a state machine to subsystems and entire systems. One can model arc

No, why would you think that? One can model in UML anything between a bunch of classes, to a state machine to subsystems and entire systems. One can model architectures in advance or after the fact. One can model while brainstorming or when discussing a design with another developer on the whiteboard.