If you're asking an expert in the area of what the topic is about, or stakeholders, or those that maybe have that topic in their circle of competence, then why would it be considered bullying? You'd expect them to have an opinion or some sort of feedback.

If you're asking someone who has literally nothing to do with that area of your work then, that's just kind of a weird situation. The key is tying the question to the area that is impacted by the person you're asking. It could be an open ended question and not even super specific.

Really asking a colleague his/her opinion on work related decisions is potential bullying now?

No, unless you're only doing it to one person or being a jerk about it.

How so?