A: This may not be an automatic technical. If it was official's error in not counting the players, the official may send a player off with no penalty. It may be called a technical. From the interpretations manual (there are several other examples under Article 36 in the interpretations manual as well):
36-5 Statement. If the officials discover that more than 5 players of the same team are participating on the playing court simultaneously, the error must be corrected as soon as possible without placing the opponents at a disadvantage. Assuming that the officials and the table officials are doing their job correctly, 1 player must have re-entered or remained on the playing court illegally. The officials must, therefore, order 1 player to leave the playing court immediately and charge a technical foul against the coach of that team, recorded as 'B1'. The coach is responsible for ensuring that a substitution is applied correctly and that the substituted player leaves the playing court immediately after the substitution.