It's certainly some inappropriate kind of intimidation, but the concept of prior restraint includes some claim that the person is forbidden from doing something, and it typically pertains to speech acts rather than to the distribution of functional tools. "He better watch out" from the AG is certainly a serious threat, but its meaning is too vague and implicit to reach the level of a prohibition or to definitively pertain to speech acts.
Sort of by definition, prior restraint is when the government prevents someone from doing something (in the context, of the term, generally always speech/expression) prior to it happening.
This is the kind of bluster that has certainly become more common in recent years, but has to some extent always been part of political theater. You'll see the same kind of thing every now and then if somebody tweets about how they'd love to feed a political figure into a wood chipper, or that the government should be launched into the sun. The Secret Service or some executive official will post that they're "investigating the matter and will take all available action", only for it to turn out that the comment was obviously protected speech.
This doesn't seem to be true. Implications of Government speech are not taken lightly and I can see examples of "informal censorship" including implied threats of legal action being classed as prior restraint. Pretty moot given today's US legal environment though.
"Justice William J. Brennan Jr. delivered the majority opinion that stated that the actions of the Rhode Island commission to Encourage Morality in Youth were unconstitutional due to their actions violating the First Amendment by placing a prior restraint on free speech. Justice Brennan's opinion stated that the commission's practice of notifying book distributors and retailers about "objectionable" publications, combined with implied threats of legal action, effectively made a system of informal censorship."
