I like this term, only because I find it a bit comical to call an inanimate object “dumb”. But rest assured, I’d be careful to never call a wine dumb to the winemaker’s face — as you can imagine, this is not a term winemakers want to hear.
So what does dumb mean when it comes to wine? It means the wine hasn’t opened, it’s not reaching its full potential and there’s a good chance it never will.
Something happened during the winemaking process that stunted the wine, or made it closed and unable to open to where the wine drinker thinks it should be.