Semantically speaking, it wouldn't be compelled speech if the CoC said simply to not misgender someone. But the fact that the CoC specifically states that writing your communications to a person who uses controversial pronouns in a way that avoids the pronoun issue alltogetheraltogether is also not allowed, even the semantics argument is invalid.
Normally rules regarding pronouns simply forbid the use of the wrong ones. There is no part that states you HAVE to use them when asked to. Thus you can avoid breaking the rule by simply not using any pronouns when communicating with someone.
This is basically a loophole. But this loophole makes the rule not compelled speech since you technically have a choice to not use them.
However, since the SE rule specifically plugs this loophole, now it becomes the very definition of compelled speech. As in, you are to speak a specific way to and about someone or be punished. You have no other choice.
As it stands written, if a user reveals their perferredpreferred pronouns, this user can effectively compel other users to use them or face punishment.
If you were to remove the part of the rule that plugs the refraining loophole, then things would likely be settled on this front.
EDIT: A user on another question pointed out another possible loophole that could resolve the compelled speech problem. There is nothing in the CoC that says you cannot just ignore a user who reveals controversial preferred pronouns. You know, the Silent Treatment.
NOTE: The compelled speech problem is only resolved by these loopholes if being a "Rules Lawyer" is permitted in this case. If being a “Rules Lawyer” is not allowed, then we are back to square one.