I would probably stop talking and look at my husband until he is done and then continue to answer the question.

Then when we're alone, I'd bring it up.

We already have an established boundary of not interrupting each other, and if we miss it, we clean up the mess by asking for forgiveness, in private!

Someone else might touch his arm to indicate that he's crossing an already set boundary saying something like, "the question was directed at me, I'd like to answer it." Said kindly and calmly.

I would NEVER chide him in public. I don't even do that in private.

It's one thing to assert a boundary, but it needs to be done in kindness. She wasn't kind. It doesn't seem like she has asked him for what she wants, she sounds like she's asserting an unspoken boundary, meaning, she hasn't actually given him the chance to agree to not do that. Getting angry or annoyed and chiding someone for crossing our boundaries are not the same as making an agreement about how to treat each other.

This is why I strongly recommend Alison Armstrong's stuff, because she goes into detail about how to make deals and assert boundaries in a healthy way that works for both men and women. Frustration doesn't work, kindness does.