You can get moire if the resizing of the image has a highly patterned area that loses resolution through resizing. It does not happen often, but is the same reason you can see moire in an image on your computer screen and have no moire when you zoom in to look closer.
The opposite could also occur. You could have a little moire in an image and have it simply be blurred so no moire is visible with a resized image.
This should not be a big deal - just something to be aware of with resizing to a small output. If you run into the issue you can change the size or quality of the JPEG and probably produce an image without moire (assuming you have a RAW file).