If I got this right, you have a "PLAYER WINDOW" right before revealing the chaos token, where you can trigger it. As you are already in the "FIGHT"-action, no "ATTACK OF OPPORTUNITY" is made by the monster.
Not strictly accurate, though the end result is correct.
No "Attack of Opportunity" takes place because the use of the trigger ability is not an Action. "Attacks of Opportunity" are a response to an Action, except for a sub-set of actions (Fight, Evade, Parley or Resign).
So the "Attack of Opportunity" doesn't occur, not because you are already in the FIGHT action, but because the use of the trigger ability is not an Action, so doesn't satisfy the condition above.