M_Natas
Hero
Of course the DM decides, if a creature takes the dodge action"The game mechanics" decide whether or not the NPC is goaded into attacking. So that fits with your first line.
If you mean the GM decides, well that's not true if you apply the D&D combat rules as written - the GM can't just decide that a creature dodges a PC's attack, or is not scared by the Battle Master using Menacing Attack.

Ingame, an attack is an attack, if that Hits it Hits. That is not comparable to speaking and having the exact same 100% reaction.
And I already said, that player characters and monsters can impose ninmagically certain conditions on others that can reduce or increase their options. But they don't controll the characters Intent.
As others have pointed out, earlier editions had morale rules that worked similarly.