Almost the same thing happened to me but it was through messaging.
One day, i was happily accepting cultural treaties and offering some. then the following day, those whom offered me and those whom I offered said that the following two things:
[to those who offered me]: Why did you cancel it?????
[those whom I offered it to]: Why did you send a trade treaty request???I though you want a cultural treaty.
btw, another strange incedent, I listed all the players who still don't have any cultural treaties with me and tried to message them, but the only options were: Message and Trade Treaty. (these people were from the alliance).