everyone is wording this kinda weirdly. officers dont have the ability to send messages to people in their regiment via teamchat - it only shows to other officers (they can however read messages from all other subclasses, but no subclasses can read teamchat from an officer)
I don't think he was saying you were wrong, I just think he did not understand it because of the way you worded it.
Also: I am pretty sure Forza meant that when typing in team chat (which is done by pressing u) no longer sends messages to people in your regiment, only people in your specific sub regiment. Making it difficult to communicate it with your team.