For example -
Questioner: What do I need to know about the system of emigrating to New Zealand? I hate the weather here...
Answer: Moving to New Zealand because you hate the weather isn't a good reason to emigrate...[continue to express their opinions on your decision].
Instead of addressing the question, the answering individual decides to express an unsolicited opinion on the decision or motivations for the person asking for advice about a particular action. The questioner didn't ask his opinion about the reason why he is emigrating, but more so 'how' to emigrate.
This type of behaviour tends to be very commonplace in both the real world and in online forums.