I think it might be the feeling of "not guy" enough rather "not understanding the particular bro culture around something."
I work in a high tech startup field that's highly bro-like on one side and very non-bro like on the other. It's interesting to watch these clashes but for the sake of our survival as a species we have to really help men extricate themselves from this stupid bro-culture.
I've been in your husband's shoes many times. You know what I like doing? Spending time with my partner and children. I like to go hiking, make photos, play music. I like the Olympics more than sports teams, and yes, I know how to use a chainsaw.
I'd rather sit around a fire with other men talking about raising our kids or how to be better men or partners, or even how to bake bread than being a bro.