Maybe?
So when we use the word "economics" we normally mean the discipline, the method of analysis and explanation. But when we talk about "economic phenomena" we normally mean not an intellectual enterprise, but actual stuff happening in the social world (eg certain sorts of dealings, and the emergent consequences of those).
"Politics" and "political" exhibit similar usage but with even more crossover: politics can refer to both the discipline, and the social phenomena it studies; and political can describe both an attempt to communicate a point of view, belief or opinion, and an event or phenomena that involves social organisation and power and hence is apt to be studied by the discipline of politics.
When someone says that all, or most, art is political I don't normally take them to mean that it is all manifestos. (Which I think would be an implausible claim.) I take them to mean that it is all, or at least mostly, a manifestation of social organisation and power and hence apt to be studied by the discipline of politics.
There are artistic movements that aim at closing the gap - ie that hold that, because all art manifests social organisation and power and hence is political in that sense, it is therefore better to take self-conscious control and make it manifesto and hence political in the communicative/intellectual sense. Socialist realism would be one such movement; futurism and vorticism are also candidates, I think.
But you don't have to adhere to that sort of movement to think that art is political in the sense of apt to be studied by the discipline of politics because part of the way social organisation and power manifest and propagate and generate the effects that they do.
