In the passive voice, you're absolutely correct it would be "It is misspoken". That aligns with what I was earlier saying about have (or another helping verb like is or am). If you're correcting someone that his words are misspoken (rather than mistyped), then misspoken would be correct.

I read this as him expecting you to correct his word choice. "I mistyped" is correct. "I misspoke" is correct. "I misspoken" is clearly wrong. Therefore, if you're wondering which word is correct in his original sentence, it is misspoke and not misspoken.

If you're referencing word choice in the original statement (which is how I interpreted his statement), you'd write "the correct word is mistyped, not misspoke"

If you're referencing "it" as the statement made/typed, you would write "that statement was mistyped, not misspoken".

Point being, as with most pedantic debates, that both can be correct depending on interpretation.

Which both makes me a fool for correcting you, and you a fool for initially correcting him, when his usage was perfectly within bounds, just didn't match with how you chose to interpret his pronouns.