Disinformation: It's History is correct from the context of the piece. i.e. the piece isn't about the history of disinformation, but rather, how history is relevant to disinformation. Just look at the sub-title:
> But history can help to disentangle the unprecedented from the historical.
That said, the author (or maybe an editor) could have avoided any argument by not using a contraction instead of trying to be punny.
The author might mean "it is history" - i.e. it is no longer a thing. Somehow I doubt that ...
> Rather than seeing the last five years as an anomaly, what happens when policy makers see this is a historical problem that is here to stay?
I interpret the title as "it is history" in the sense that disinformation is historically relevant, and as such it is a valid field of historical studies.