There may be a "disconnection" between what he thinks he's playing, and what you know we're playing.

He may think he's playing a RPG (since it's both labelled as a "Final Fantasy" and a "mmoRPG") in which there would be many valid ways to play.
We know it's actually not the case and all the RPG coating is just for show. There is only one way to play a job.
Thus, what you said may appear rude to him because it looked like you were trying to restrict him, when in reality it's the game that's restricting us.

The solution to this problem can only come from the developers :
- stop pretending it's a RPG to avoid misleading new players (the dev panel about battle design at the fanfest earlier was totally disconnected from the reality of the game)
- admit there is only one way to play and modify the game in accordance (like reducing number of actions) to avoid this kind of situation where players can do something not planned/wanted
- or (harder) actually make a RPG.