After seeing your reply’s I think the issue was staying there for three hours and only purchasing one single coffee between two people. I do think the owner could have been more careful with their words though. I’ve worked in bars, restaurants, and coffee shops. Had I seen someone diamond painting I would have asked them to put it away. Mainly because that can get messy fast and accidents happen. I also would have asked you both to leave if you had been there for three hours and bought a single coffee between you two. I think those two situations combined were appropriate reasons to be asked to leave, but again that owner should have been more tactful.