Remember my friend who makes those wild ceramic sculptures? Someone at a show called his favorite piece a 'really nice planter'. He just laughed and said, 'Thanks, but it's actually a sculpture about sound waves, want me to tell you about it?' The guy got super interested and ended up buying a smaller piece. Sometimes people just don't know what they're looking at, and a gentle correction can turn an awkward moment into a good chat. I'd say say something, but keep it light, not like you're scolding them.