It's a drawdown to claim the US military strikes on June 21st somehow triggered a 'No' outcome for Polymarket predictions on June 19th and 20th; those earlier days simply had no military action, which is what actually caused their resolution.
That 'No' outcome was decided the moment nothing happened on those specific dates, regardless of what came later.
You can't cause something not to happen in the past by doing something in the future, like saying my neighbour winning the lottery today caused my ticket not to be drawn yesterday.
The market resolution was a fail-safe of no activity, not an effect of a later event.