The slider used by the Custom Query Widget is FlexSlider, not Bootstrap Carousel. Button navigation is not yet supported but planned for a future version.
A query of multiple pages is supported. The slider from the theme demo is an example of this. You can read more about the widget in this tutorial and you may also find this one useful.
So I have been following the instructions in the tutorial, however my slider is not appearing with the arrows. What am I doing wrong?