I've decided that I'm done being pissy about this kind of response, or thinking that it's something that can be coached away. I choose to look at it like any other cultural communication difference - something that you learn about, try to give some grace to, and work a little harder to bridge (unless you're defusing a bomb, performing surgery, flying an airplane etc.).

In this person's communication culture, they are saying "I don't know, but here's my attempt to help."

For me, it really comes down to is whether or not I believe the responder is acting in good faith. If you can't assume good faith, the shape of the response isn't the actual problem.

Of course, my opinion of them is also related to how often their interpreted answer or conversational contribution is "I don't know", and how often they choose to interject with that when it's not necessary. I suppose the latter is cultural too; perhaps I should be clearer in open forums whether I expect them to answer.