I understand if you don't like how the person phrased it, but the goal of the DM was obviously to get the store owner to replace the AI poster. Assuming that they would have gone on a crusade because they didn't pick a "preferred artist" is pure unsupported speculation on your part.

It comes across as spiteful, I don't think it is at all obvious and it isn't obvious to the store owner either.

We just disagree, and that's why this is the wrong approach to enacting whatever kind of change they wanted.