Graffiti by mistake

In the researches of graffiti art in Catalunia and the ways of express of the Catalan street artists I discovered a strange way of "fight" against graffiti art in the public spaces. The "covering technique".
Authorities try to paint it out the graffiti, as you will see next, and because of that the result it looks actually like a work of art. They don't realise that by not using the same color like the support they actually make nice interventions in the public space.
Even that I like this nice minimalism wall I can't imagine how they think that by making another intervention on the public wall, it is different then the original graffiti work effect: the painting of a public wall?