They have introduced a red herring into the conversation.
A red herring is something that misleads or distracts from a relevant or important question
a fact, idea, or subject that takes people's attention away from the central point being considered
If you like to use a Latinism, you may say that they have made a non sequitur
a statement (such as a response) that does not follow logically from or is not clearly related to anything previously said
We were talking about the new restaurant when she threw in some non sequitur about her dog.
The person may also be facile (in its insulting sense rather than in the sense of doing things easily and with little effort)
Ignoring the true complexities of an issue; superficial
If the complexities are large, ignoring them is almost the same as ignoring the whole issue.