If OP's DH is anything like my dad and this is a pattern, I don't see how what DS did was so terrible. Rude? Yes. But sometimes that is literally the only way available to shut someone down. And I would have cheered my mom's praises to the sky if she had ever stood up for me like that, but she avoided conflict at all costs.
I know we're all coming at this from our own angle and with our own experiences coloring our reactions, but I honestly don't see the need to "shut someone down". It seems to me that the OP's husband and your dad were just trying to make a connection with their child and were rebuffed. If I was the dad, I'd be hurt too. Instead of shutting them down, why not engage them, ask them questions, and relate it to your own interests?
Again, coming from personal experience.
If I did nothing: I'd basically be held hostage for at least half an hour nearly every day while he talked and I had to feign interest.
If I tried to related it to my interests: I'd be a horrible person because he was talking about this
and I'd get a half hour tirade about how horrible and rude I was. Or I'd be told that under all the superficial stuff, they really are the same, you know.
If I tried to tell him politely that now wasn't the best time/I'm on my way out the door to work/have other things to do: I'm a horrible person because he's just trying to help me and how dare I be so rude as to not listen to him.
If what he was saying was factually incorrect and I had proof: I was horribly rude because he'd heard it from someone who had a niece who did that for a living, and that's not what this guy he'd just met said it was like, and I'd get a lecture on how my take on things (studying directly from experts in the field, no less, and with the course materials to back me up) was completely unrealistic and how dare I question what he just learned that day, despite the fact that I'd been studying it for two semesters.
No matter what I did, unless I shut him down quickly and left the area quickly, I'd basically be treated to a half hour or longer lecture on whatever it is that he heard about, whether or not it was relevant to my interests. My dad never quite understood why I never wanted to hear about his friend's daughter the kindergarten teacher because teaching five and six year olds is really the same as directing a high school band, under the superficial stuff. Um, no it's not. Plus the ideas he had for my schooling, my career, and what I wanted to do where not the same ideas I had. He was trying to push me into things that I had no interest in, and I didn't have time every day to listen to his lectures on whatever thing was the newest and best thing for me to do. If I didn't shut him down quickly, I was a captive audience. He even followed me to the bathroom when I walked away. If I did shut him down, I was rude and unappreciative of whatever fountain of knowledge he was spouting.
Don't get me wrong, there were some days I listened to him and we had a good conversation about things, but most of the time I was in for either him blowing up at me because I was a horrible person and never listened to what he had to say or was treated to a lecture for over half an hour that had nothing to do with either reality or what I was interested in.
And yes, this is part of the reason I've given him the cut direct. I just don't deal with it any more.