Free speech debates around this are ridiculous as this was in a school setting.
If this was taking place in the public space, then fine. But as a teacher you can't just go around saying whatever you feel like and then claim your right to free speech in order to justify your actions. As with any job, you have to act professionally and that often means biting your lip/finding tactful ways to articulate certain topics.
Not getting into the "should he/shouldn't he have" debate, but justifying on the grounds of free speech is nonsense. That's not the issue here, as it was with CH.