On the other hand....Regardless of belt color, I don't know that at a large seminar working on solo weapons I'd be very open to a stranger telling me I'm doing things all wrong...
Belt color is kind of nice when you are a beginner and looking for someone better than you to train with. That guy was a brown belt, likely the same or close to the same rank as you at 1st kyu. If he didn't ask, I wouldn't tell, if I were you.
I've often thought about adding blue and brown belts to our class ranking. But it's not really that important. It kind of
makes students feel good, kind of
helps new people judge who has a more informed opinion, but I also think colored belts are kind of