Probably means there were two patchs of cellular rain, concentrated in a small radius of about a kilometer. Rainbows appear when sunlight is scattered from rain drops or drops of water, like near a waterfall. Since rain absorbs light, they are generally only visible from out side the rain patch. It is pretty common to see completely circular rainbows when flying over rain clouds. You will generally only see a rainbow when the sun is at your back and the rain storm is in front of you, will little or no intervening rain.