That does mean that I would not automatically jump to conclusions about Russia or war or whatever; since much of national public policy is presented today, it's also a popular day to express disagreement, and apparently some farmers had already announced they would be doing so today.

(I'd assume the BBC reporter to be aware that Prinsjesdag is today, and that they'd mention that fact in this article, but apparently not.)

You'll find the answer in who is organizing these groups.