"It was really amazing. I mean, he'd never mentioned that he played in the symphony, like serious violin playing, not fiddle playing. And he just blew us away"

This quote is referring to an individual who had a concealed skill that was exposed to the speaker and their friends. The speaker was shocked to discover that the individual was a severe violin player, not simply a fiddle gamer. The speaker was surprised by the person's ability and talent, and the fact that they had never ever mentioned it before. It was an enjoyable surprise to the speaker and their good friends, and the person's performance was so remarkable that it left them all in awe. The speaker was plainly impressed by the individual's ability and the reality that they had actually kept it concealed until that moment. It was a minute of surprise and admiration for the speaker and their buddies, and it was a moment that they will likely keep in mind for a very long time.