It would be nice if the paper had determined (or, if the city had shared, since they were apparently asked point blank) whether or not it broke the laws, that would seem to be the key issue. City code can be inscrutable at the best of times, but that's the important thing, not whether the City isn't prioritizing what is perceived to be important by some rando twitter account.
If it's legal, I have no issue with them doing it or frankly anyone else doing the same thing.
I work in marketing for a non profit and we've done this with chalk and stencils for big events, but only in cities where we knew it was legal. I suspect this is the same material we used, which washes off after the first rain or next time the sprinklers run.
The claim they used paint, maybe the firm they hired used something different. They’ve already started painting over them. I just wonder if everyone chose to do this ...what would it look like?! Semi-permanent or not. I guess it doesn’t matter what they’re saying about you as long as they are talking about you:/