Clouds and rainbow? Is this for real?

The caption accompanying the photo (from the UK Telegraph photos of the day): “Melissa Rensen took this photo of a rainbow through the plane window as she flew over the Carribean Sea. But Melissa, from London in Ontario, Canada didn’t even realise until she looked at the images later on. She was travelling from North America to Hounduras and spotted an interesting cloud formation below. And after looking back at the shot she noticed the blanket of colour covering the expanse below.”

It looks odd — rainbows sometimes come in pairs, but they are then separated. Yet the this seems to have a continuous repeat of the spectrum.