It all depends on how you think about the question. First of all, just because something is wrong doesn't make it illogical. A false conclusion does not equate to a logical error.
All cats are animals.
Therefore, all cats are green. This problem is logically sound, but one of the premises is untrue. Hence the problem. Not that it really matters, since mathematics and logic are different anyhow. It all depends on how you think about the question.