That is a crazy reason for a technical, because you really don't have to put in a sub. there is no rule that you have to have 5 players out there. you can resume play with only 4 players on the court. don't know if that is a legitimate reason for a "T" or not.
You need to read your rule book again. If you have 5 available players you must put 5 on the court. After a player fouls out, the coach has 20 seconds to replace that player , provided he or she has a player available, or it is a technical foul.