How to interact with colleague who will happily talk about a thing, but from the way he talk about it, it becomes clear, that he does not fully understand some underlying concepts - but at the same time is not that kind of personality, that would ask for clarification or explanation (maybe because it is sign of weakness).

There is difficulty involved in such a situation, since such people will demand to be consulted in a decision process, but instead of brainstorming solutions one will need to neutralize the diffusion of the concepts first, and when this is done time is already up and solution cannot be brainstormed any more.

Maybe FUD is not the correct acronym, maybe DIS, Diffusion, Indifference, Surety.