Fun fact: propaganda used to be a morally neutral term [0], which we now call "public relations", after the word took on connotations with Nazis and Soviets. Everyone who is advocating for a policy, moral position, etc., is putting out "propaganda"; by any objective measure, MLK and Thomas Paine were extremely effective propagandists, and we (rightly) celebrate them for it.

The real question is, what one is advocating for, and whether one does so honestly. And while there are certainly circumstances for justified violence, "antiwar" seems like a pretty good thing to advocate for, all else being equal. And I fail see any blatant dishonesty or bad faith in this piece, whatever the shortcomings might be of The Guardian or the mainstream press in general.

[0] https://en.wikipedia.org/wiki/Propaganda_(book)