Black flag? Don't you mean false flag? Black flag means that it is dangerous to be outside. False flag is a military operation where you change your flags to infiltrate the enemy and create chaos.
If this were a "false flag opperation", to what end? If it were for a military attack, we could have gone into Iraq or North Korea at any time. Afghanistan is not a country with a military significance beyond breeding ground for terrorism (and that LONG before we put our first foot on that ground).