If, at 6 months of dating, my BF showed up unannounced at my workplace which is 30 minutes out of the way simply because we hadn’t seen each other in a couple of days, I would be EXTREMELY uncomfortable and it would majorly creep me out. It would be a WTF are you doing here moment for sure.
I am one of those people who keeps their work life and personal life separate.
You drove 30 minutes out of your way, showed up while he’s on the clock and wanted to hang out for 10-15 minutes while you bought art supplies that you probably would have normally bought someone closer to you?
You spent an hour in your car to see him for 15 minutes.
This is a sweet gesture but not everyone takes these things the same way and I would have at least ran it by him or given him a heads up that you were on your way in. He could have been with a customer or with his boss when you showed up. Or he could have taken his break or lunch at that time and you would have had more time together.
I would also talk to him about your relationship. It seems like you may be more invested/on a different page than he is and/or that you are not aware of his preferences for this relationship.