Perhaps they were just speaking theoretically. We could do Z if M happens.
IANAL, but I think you actually have the means to carry it out for it to actually be a crime. Just talking about what you “should do” or “want to do” is hypothetical, especially if you can’t realistically do it, and thus not a threat.
But I don’t know all the details of what was said, or whether they had the weapons or the boats.